fix(apple): engine starts leave the main thread — input never waits on the audio server

An AVAudioEngine start can block on the audio server for seconds (~1.9 s
per attempt in the 2026-08-14 field case), and macOS captures and sends the
stream's input from the main thread — so every device-change rebuild, loop
or no loop, froze the stream's input for the length of the rebuild, and a
mic-on session start stalled the UI at connect.

All engine lifecycle work (start/startEngines and below, teardown, rebuild)
now runs on a per-session serial engineQueue; the main queue keeps only the
trigger bookkeeping — debounce, backoff, and the retry ladder — which is
cheap by construction. The rebuild path splits accordingly: rebuildFire
(main: bookkeeping, reads the config) → performRebuild (engineQueue: the
actual teardown + start) → rebuildFailed (main: ladder scheduling; a fresh
trigger already queued wins over a retry).

Confinement moves with the work: ring, startConfig and enginesAttempted go
under the existing stateLock (start paths write on engineQueue, stats and
the revive gate read elsewhere); combinedGate is engineQueue-confined; the
permission-grant continuation lands on engineQueue instead of main. The
engines were already lock-guarded and stopped cross-thread by stop(), and
every start path already re-checks the stop flag after publishing, so the
in-flight-start-vs-stop race keeps its existing resolution.

Embedder-visible edge: SessionAudio.start() is now asynchronous on macOS
too (it always was on iOS/tvOS) — playback is live shortly after the call,
not on return; stats is safe from any thread.

Gates: swift build + 295 tests 0 failures (macOS), full-package
arm64-apple-ios17.0 typecheck.

CHANGELOG.md

@@ -12,7 +12,82 @@ with the version table of the release you are moving to, then read **Breaking ch
 
 ---
 
-## v0.28.1 — in development
+## v0.28.1
+
+50 commits since v0.28.0.
+
+A patch release in the strict sense: **nothing on the wire, in the C ABI, in the driver protocol or
+in the plugin contract moves.** Every host, client, driver and plugin built against v0.28.0 keeps
+working against v0.28.1 and vice versa, in both directions and with no re-pairing.
+
+### Versions
+
+| | v0.28.0 | v0.28.1 | Notes |
+|---|---|---|---|
+| Wire protocol | 2 | **2** | unchanged |
+| C ABI | 19 | **19** | unchanged — `include/punktfunk_core.h` is byte-identical to the v0.28.0 tag |
+| Rust edition | 2024 | **2024** | unchanged |
+| MSRV (`rust-version`) | 1.85 | **1.85** | unchanged |
+| Workspace crate dirs | 27 | **27** | unchanged |
+| Virtual-display driver protocol | 6 | **6** | unchanged (minimum accepted still 3) |
+| Windows virtual-gamepad channel | 3 | **3** | unchanged |
+| Plugin index schema | 1 | **1** | unchanged |
+| `api/openapi.json` | 0.27.0 | **0.28.0** | the management API **did** change (two collection deletes, below); the file carries the stamp it was regenerated under, not `0.28.1` |
+| gamescope patch level (`+pfhdrN`) | 6 | **7** | 8 patches → 9 (the linger crash); no new capability |
+| `@punktfunk/host` (SDK) | 0.1.4 | **0.1.4** | unchanged |
+| `@punktfunk/plugin-kit` | 0.4.1 | **0.4.1** | unchanged |
+
+⚠ **The `api/openapi.json` stamp is not a per-release counter** and should not be read as one. The
+drift test (`openapi_document_is_complete_and_checked_in`) normalizes `info.version` on both sides,
+so only the *surface* is gated and a version bump alone never invalidates the snapshot. The table
+row says what the file actually says. Regenerating it needs a Linux or Windows host build —
+`punktfunk-host` does not compile on macOS.
+
+### ⚠ Breaking changes
+
+**None.** No wire change, no C ABI change, no driver-protocol change, no plugin-contract change.
+Three things are worth an embedder's or packager's attention anyway, none of which break a build:
+
+- **The Rust crate gained one public constant.** `punktfunk_core::client::FLUSH_COOLDOWN` was
+  `pub(crate)`; the host now compares against it rather than against a copy of the number (see the
+  keyframe-cadence fix below). Addition only.
+- **`NativeBridge.nativeStartAudio` takes a third argument** on Android — `isTv`. Detail in the
+  Android section; this is a JNI signature change, so an out-of-tree caller must pass it.
+- **Every Linux packaging channel now ships a second gamescope artifact**, the Vulkan WSI layer,
+  and a package that carries the compositor without it is *fatal* rather than degraded. If you
+  repackage `punktfunk-gamescope` downstream, read the gamescope section before rebuilding.
+
+### The management API gains two collection deletes — "unpair all"
+
+Clearing a host's trust store meant one row-level delete per device, each with its own
+confirmation. Two new endpoints, one per pairing plane:
+
+```
+DELETE /api/v1/clients          -> {"unpaired": N}
+DELETE /api/v1/native/clients   -> {"unpaired": N}
+```
+
+They are **not** a loop over the per-fingerprint deletes. Each empties its store in ONE persisted
+write, because N deletes would rewrite and atomically rename the store N times and a failure
+partway leaves a half-emptied store with nothing saying which half. The two planes are separate
+endpoints because they own separate trust stores with separate persistence and separate revocation
+duties.
+
+Being collection deletes, they carry the single delete's revocation guarantees across the whole
+set: a live session owned by any removed certificate is ended, and on the GameStream side the ENet
+control port (UDP 47999) closes, because no pairing is left to hold it open.
+
+**200 with a count, not the single delete's 204/404.** "Unpair everything" is idempotent — an
+already-empty store satisfies it — and the count still distinguishes three devices from none.
+
+⚠ **Both are admin-token only.** The route-classification gates match on (method, path), so the
+roster's plugin-readable `GET` does not carry over to emptying it; both new routes have explicit
+rows in the table, like every other pairing-administration route. The native endpoint answers
+**503** on a host built without that plane, which is why the console calls only the planes that
+actually have a row.
+
+`UnpairAllResult` is the one new schema. `api/openapi.json` is regenerated;
+`docs-site/public/openapi.json` is re-synced from it (see **Documentation** at the end).
 
 ### The pad-audio "Wireless Controller" speaker hides while no client pad is attached
 
@@ -66,6 +141,38 @@ Punktfunk only takes it for the duration of a stream. If you *want* apps to reco
 while idle, select "Punktfunk Microphone" manually; the host no longer re-asserts it (idle
 re-assertion used to stomp a manual choice within one mic-pump reopen).
 
+### The NixOS module started a second host in root's systemd, which stole the ports from the real one
+
+Found on the first real deployment of `packaging/nix/nixos-module.nix` (NixOS 26.05, punktfunk
+0.28.0-nix). The host crash-looped forever on one line:
+
+```
+ERROR punktfunk_host: start RTSP server: bind RTSP 48010: Address already in use (os error 98)
+```
+
+`systemd.user.*` has no per-user form in NixOS: it installs units into **every** user's systemd
+manager. `host.autoStart` then adds them to `default.target` — for every user, including **root**,
+whose `user@0.service` springs into existence the moment anybody so much as SSHes in as root. Root's
+copy of the host won the race for the fixed ports, and the desktop user's copy could never bind.
+
+The failure is nastier than it sounds because every *other* listener binds first and logs success —
+the version banner, mDNS on 47989, the GameStream warning all print normally — so the log reads like
+a conflict with some unrelated program. A second copy of *itself*, running as root, is the last
+thing anyone looks for. `host.users` did not help: that option only granted `input`/`punktfunk`
+group membership and never scoped the units.
+
+Fixed by rendering `ConditionUser=` on all four user units (`punktfunk-host`, `punktfunk-web`,
+`punktfunk-web-init`, `punktfunk-scripting`) from `host.users`. Each entry is written `|user` — the
+pipe makes it a *triggering* condition, which systemd ORs; plain repeated `ConditionUser=` lines are
+ANDed and would have matched nobody. With `host.users` empty the units fall back to
+`ConditionUser=!@system`, which still keeps root out while leaving a normal login free to run the
+host by hand, as the module header documents.
+
+`packaging/nix/module-check.nix` gained three assertions covering both branches and the fact that
+`punktfunk-web-init` keeps its pre-existing (non-triggering) `ConditionPathExists` alongside the new
+condition. They run in the `eval` leg of `nix.yml`, and were verified to fail against the unfixed
+module before being committed.
+
 ### The Steam plugin synced nothing on Windows: its art is in Program Files, the art roots were not
 
 Field report — the plugin installed, the grid stayed empty, and the only clue was one host warn per
@@ -110,6 +217,39 @@ silence would be the wrong answer.
 expect art, the cue is the host log's `dropped local art the proxy may not serve` line, and the knob
 is `PUNKTFUNK_LIBRARY_ART_ROOTS` (which **replaces** the defaults — list every root you need).
 
+### Hyprland/Sway — the wlr-family backends asserted a cursor mode instead of negotiating it
+
+🛑 **Every cursor-forward session on current Hyprland died at `select_sources`** — "pipeline build
+failed" and a black client, with `unavailable cursor mode 4` in the portal log.
+
+Hyprland and wlroots both hardcoded portal `CursorMode::Metadata` whenever the session had
+negotiated the cursor channel, and never asked the backend what it supports. That is **not** a soft
+failure: xdg-desktop-portal's **frontend** validates the requested mode against the backend's
+`AvailableCursorModes` and fails the call with `"Unavailable cursor mode %x"` before the backend
+ever sees it.
+
+⭐ **Measured on glass 2026-08-14, and worse than the report suggested.** Against a live Hyprland
+0.56.2 with xdg-desktop-portal-hyprland 1.4.1 and xdg-desktop-portal 1.22.1 — all current —
+`AvailableCursorModes` reads **3** (`Hidden|Embedded`) on both the backend impl interface and the
+frontend. **xdph does not offer the metadata cursor at all**, so this broke every cursor-forward
+session on current Hyprland, not merely on old installs, and **updating the portal would not have
+helped.** xdpw is the same from the other end: its `screencast.c` refuses `METADATA` outright.
+
+`pf-capture`'s own portal path has always negotiated (`choose_cursor_mode`); this restates that
+ladder in `pf-vdisplay`, which may not depend on `pf-capture`. The downgrade is graceful rather than
+merely survivable: with the portal on `Embedded` no `SPA_META_Cursor` arrives, so the host feeds the
+cursor channel nothing and a cursor-forward client draws nothing of its own — **one pointer, not
+two.**
+
+**`PUNKTFUNK_PORTAL_CURSOR_MODE=auto|hidden|embedded|metadata`** pins the preference for a backend
+that advertises a mode it implements badly, which negotiation cannot detect. It is a preference
+only: a pin runs the same ladder, so no value can re-create the refused request.
+
+⚠ The module is declared **unconditionally**, so its ladder tests run on every CI leg rather than
+only the one that compiles `mod hyprland` — including a Linux-only test pinning our bit values
+against ashpd's enum (ashpd answers 4 for `Metadata`, the number in the report), verified
+non-vacuous by planting a wrong discriminant.
+
 ### Android — the audio plane trusted AAudio, and a TV box that opened a stream it never played was silent for the session
 
 🛑 **Reported from the field: no audio at all on an NVIDIA Shield Android TV, stereo, with the same
@@ -160,6 +300,84 @@ existing `debug.punktfunk.no_av_sync`: `debug.punktfunk.audio_sharing` (`exclusi
 old give-up-on-disconnect behaviour). A stream that stops taking samples after it started now says
 so at `error` level instead of looking exactly like an app with no sound.
 
+### gamescope — we ship our own Vulkan WSI layer, so a game can reach an HDR10 swapchain (⚠ packager-visible)
+
+🛑 **On essentially every box running a distro gamescope, no game could render HDR at all** — and
+nothing said so.
+
+A game nested under gamescope gets an HDR10 swapchain from the FROG WSI layer and from nothing
+else: gamescope advertises no runtime colour-management protocol a Mesa/NVIDIA WSI could negotiate
+through. That layer speaks `gamescope_swapchain` to the compositor, and when the two disagree the
+compositor rejects the client's `swapchain_feedback` and **every Vulkan client dies on a black
+screen** with sound and input intact and no error anywhere.
+
+We shipped our own compositor and *not* a layer, on the recorded grounds that the layer is
+"version-independent of the compositor binary". It is not — `wsi_layer_matches_our_gamescope()`
+exists precisely because it is not — so the host was left guessing from version triples, and that
+guess is wrong in both directions. A distro at the same upstream tag that patched the protocol
+compares EQUAL and keeps a layer that will black-screen every game; a distro at a different tag
+with a byte-identical protocol compares unequal and loses HDR for nothing. **Since we pin a rev,
+the second case is the normal one.**
+
+We now build the layer from the same tree at the same rev as the compositor and ship it, so the two
+cannot drift and the guess stops being load-bearing. It installs under **our own** name
+(`VK_LAYER_PUNKTFUNK_gamescope_wsi`), at our own path, with our own enable/disable variables, so it
+coexists with the distro's rather than colliding — the Vulkan loader keys implicit layers on that
+name — and the host switches the two independently within one session.
+
+`WsiPlan` resolves three states once per launch (the fallback spawns `--version` probes):
+
+| state | condition | action |
+|---|---|---|
+| `Ours` | our layer is installed | enable ours, force the distro's off — **both halves, or it is a bug** |
+| `DistroKept` | no layer of ours, distro's looks compatible | touch nothing |
+| `DistroDisabled` | no layer of ours, distro's untrusted | v0.28.0's behaviour |
+
+That last arm is the fail-safe: a host newer than its gamescope package behaves exactly as it did,
+rather than enabling a layer that is not there.
+
+⚠ **What packagers must know.** The layer manifest carries an **absolute** `library_path` baked in
+at build time, so every channel installs the `.so` at exactly that path: literal
+`/usr/lib/punktfunk` — **not** `%{_libdir}` (which is `/usr/lib64` on Fedora) and not a Debian
+multiarch triplet. Nothing links it by soname (the loader `dlopen`s it by that path), so multilib
+has no claim. rpm and nix read the path back **out of the manifest** and fail if it names a file the
+package does not install, because a manifest pointing at nothing is the silent shape of this bug.
+A missing layer is **fatal in every channel**, not best-effort: a package carrying the compositor
+without it looks completely healthy and then silently denies every game an HDR10 swapchain.
+
+The packaging scripts now take `--stage` (the DESTDIR the gamescope build script wrote) instead of
+a path to one binary, and CI caches the whole staged tree; the `gs-cache` key already hashes
+`packaging/gamescope/**`, so stale caches in the old single-file shape cannot be restored into the
+new layout. The manifest rewrite lives in `packaging/gamescope/rewrite-wsi-layer-manifest.py`
+rather than a heredoc, because the FHS builds and the Nix store both need it and must rename the
+layer identically. **NixOS has no `/usr`**, so the layer lives inside the gamescope derivation and
+the host's path is overridable with **`PUNKTFUNK_GAMESCOPE_WSI_LAYER_DIR`**, which the module sets
+— the same posture as `PUNKTFUNK_GAMESCOPE_BIN`.
+
+### gamescope — HDR sessions anchored SDR white a stop bright, and never said game HDR was unreachable
+
+🛑 **Field report: Steam's Big Picture UI glaring and over-saturated while HDR game content looked
+washed out, on the same stream.** Those are one error.
+
+gamescope maps everything that is not an HDR game — the desktop, the Steam overlay, an SDR title —
+into the session's PQ container at `--hdr-sdr-content-nits`, and we passed that flag **only** when
+an operator had set `PUNKTFUNK_GAMESCOPE_SDR_NITS`. Unset, gamescope used its own default of
+**400**, while every first-party client anchors diffuse white at **203** (BT.2408 reference white;
+the Apple presenter hands exactly that to `CAEDRMetadata.hdr10`'s `opticalOutputScale`). The two
+ends sat nearly a stop apart, so the UI landed above SDR white and the client's tone-mapper worked
+from a reference point the host had never used, flattening the content around it.
+
+**The flag is now always passed, defaulting to 203.** `PUNKTFUNK_GAMESCOPE_SDR_NITS` still
+overrides it for anyone who wants a brighter or dimmer desktop — it is the anchor, not a taste
+knob. ⭐ Because it is an env var, a field A/B needs **no rebuild**.
+
+Separately, and visible in the same log: the two HDR decisions in a gamescope session were made
+independently. `hdr_args()` never consulted `wsi_layer_matches_our_gamescope()`, so when the layer
+check fired the session launched **advertising HDR while having made an HDR10 swapchain
+unreachable for every game in it** — a title told to render HDR rendered it into an SDR swapchain
+and looked washed out, with nothing anywhere saying why. It now warns. The behaviour of the check
+itself is deliberately unchanged; the section above is the real fix.
+
 ### punktfunk-gamescope `+pfhdr7` — a lingered session no longer dies of its own capture teardown
 
 🛑 **On client disconnect the host keeps the headless gamescope alive so a reconnect resumes the
@@ -179,6 +397,200 @@ four coredumps on 4K60 HDR + composited cursor, zero after; disconnect/reconnect
 lingered session. Banner `+pfhdr6` → `+pfhdr7` (no new capability — but "reconnect lost my game"
 triage must be able to read a box's exposure off its banner, the same rule as `+pfhdr5`/`6`).
 
+### Apple — the stats overlay lied three ways, and every host-anchored number with it
+
+🛑 **Two sessions minutes apart on the same wire read `hostnet_p50` 17–21 ms, then a physically
+impossible 4.4 ms** — host-side encode alone is ~4.7. Three independent defects, all of which
+corrupt any measurement taken against a host clock:
+
+- **A frozen clock-offset.** The client consumed the **connect-time** skew offset and cached it —
+  in a `Stage2Pipeline` field, in a `StreamPump` `let`, and in a `ContentView` closure **capture
+  list** feeding the hostnet meter and the host/network splitter. The core keeps a *live* estimate
+  (`punktfunk_connection_clock_offset_now_ns`, ABI v10, re-synced every 60 s and on suspected
+  wall-clock steps) whose own doc says the connect-time value "silently corrupts every
+  capture-clock comparison" after an NTP step — **and a VM host steps.**
+  `PunktfunkConnection.clockOffsetNs` is now the live read (an atomic load behind the FFI), read at
+  use: per record, per AU, per enqueue. The Swift audio plane's AvSync observation takes the same
+  live value.
+- **Silently trimmed impossible samples.** `LatencyMeter`'s guard (≤ 0 after offset correction)
+  dropped samples without counting them, so a wrong offset did not invalidate a window — it trimmed
+  the impossible half of the shifted distribution and presented the surviving tail as a plausible
+  small number. That is the origin of the historical "0 ms network / 0 ms e2e" readings. Refusals
+  are now counted and drained **separately from `Stats`** — deliberately, because a fully-poisoned
+  window drains to `nil` and a count inside `Stats` would vanish with it. The HUD shows an orange
+  **`clock offset suspect`** line and the stats line grew **`skew_trim=N`**; nonzero means
+  disregard `e2e`/`hostnet` for that window.
+- **`-1` fallbacks printing as `NaN`.** In a `CVarArg` context `cond ? someDouble : -1` does **not**
+  unify to `Double` — the literal goes in as `Int`, and `%f` reads `Int64(-1)`'s all-ones bit
+  pattern, which is a quiet NaN. Latent since the 1 Hz stats line existed. All fallbacks are now
+  typed `-1.0`.
+
+⚠ **Any client-side e2e or hostnet figure recorded before this release is suspect** and worth
+re-measuring rather than trusted as a baseline.
+
+Two new levers ship with the tvOS present-floor investigation, both env-only:
+**`PUNKTFUNK_FRAME_LATENCY`** (float 0…4, default 1) makes the `preferredFrameLatency` ask
+adjustable, so an on-device ladder can establish whether the property does anything on tvOS — the
+previous "immovable two-refresh floor" verdict rested on a **readback** of a plain read-write
+float, which is not a grant. **`PUNKTFUNK_PRESENTER=stage1` now resolves on Release builds** (the
+persisted picker stays DEBUG-gated; an env var takes a `devicectl`/Xcode launch to exist, so it is
+never a leftover). Stage-1 presents on the hardware video plane rather than through the GPU
+compositor — the one rung that can dodge the two-refresh regime — and the field A/B that concluded
+otherwise had silently run stage-4, because the gate keyed on build config.
+
+### Apple — two colour faults: an SDR stream shipped untagged, and it forced the TV into HDR10
+
+- **The SDR layer was never tagged.** `configure(hdr:)` guards on `hdr != hdrActive` and
+  `hdrActive` starts `false`, so a session that is SDR from its first frame matched the initial
+  state, fell through the guard, and `configureColor` never ran once — the layer kept `make()`'s
+  bare configuration, which assigns no colour space. An untagged `CAMetalLayer` gets no colour
+  matching: a BT.709 stream is drawn in the display's native space. Mild oversaturation on a P3 Mac
+  or iPad; on a tvOS display composited for HDR it also lifts the black floor. ⚠ It also made
+  `PUNKTFUNK_SDR_COLORSPACE` **dead code on exactly the sessions it exists to fix**, so a field A/B
+  of that knob would have shown no change.
+- **An SDR stream drove an HDR-capable TV into PQ output.** `applyDisplayCriteriaIfNeeded` builds a
+  synthetic format description hardcoding BT.2020 primaries, ST.2084 and the BT.2020 matrix, then
+  hands it to `AVDisplayManager` — and its guard checked only that no criteria had been set and that
+  the user's HDR *setting* was on, never that **the stream** was HDR. That setting defaults to true.
+  The Apple TV switches HDMI to limited range in its HDR modes, so a set configured for full range
+  renders code 16 as grey rather than black. Now gated on `connection.isHDR` as well; layout re-runs
+  it, so a session that flips to HDR mid-stream still picks the mode up.
+
+### Apple — the macOS device-change recovery could answer itself forever (mic on)
+
+**Streaming from a Mac with the microphone enabled cut audio AND input on a ~2.5 s metronome
+while video ran untouched** (field, 2026-08-14: a Mac Studio whose default input is a 6-channel
+device). The chain: the voice-processing engine cannot start on that mic, every rebuild re-tried
+it, and the failed attempt's HAL churn (VPIO builds and tears down an aggregate device) stopped
+the healthy fallback engines — which posted the `AVAudioEngineConfigurationChange` that scheduled
+the next rebuild. Each ~1.9 s rebuild runs on the main thread, where macOS input capture and
+sending live, so input froze on the same beat — and since audio, input and mic share the QUIC
+datagram plane while video rides its own socket, the wire signature read as a network fault and
+the host's METRONOMIC heuristic pointed at the display stack. Three defenses, layered because no
+single one covers every feedback shape:
+
+- **A voice-processing start failure latches per input device** (`CombinedTopologyGate`): a
+  rebuild goes straight to the split topology instead of re-running a failure that is a property
+  of the device. A different default input earns exactly one fresh attempt.
+- **A configuration change posted by an engine that is RUNNING is the rebuild's own echo, and is
+  ignored**: an engine stops itself before posting, so a live poster was already restarted.
+- **Rebuilds that chain anyway back off exponentially** (`RebuildBackoff`: 0.5 s floor doubling
+  to a 30 s cap, reset by 10 s of quiet) — an unforeseen loop costs one blip per half-minute
+  instead of a metronome, and the chaining itself logs a WARN that names the condition.
+
+iOS/tvOS behaviour is untouched (routes are session-managed there; nothing is latched). Until a
+client carries this, the field workaround is turning the client microphone off.
+
+**And the engines no longer start on the main thread at all.** An engine start can block on the
+audio server for seconds (~1.9 s per attempt in the field case) and macOS captures and sends the
+stream's input from the main thread — so even a single legitimate device switch froze input for
+the length of the rebuild, loop or no loop. All engine build/start/teardown now runs on a
+per-session serial `engineQueue`; the main queue keeps only the trigger bookkeeping (debounce,
+backoff, retry ladder), which is cheap by construction. ⚠ Embedder-visible edge:
+`SessionAudio.start()` is now asynchronous on macOS too (it always was on iOS/tvOS) — playback is
+live shortly after the call, not on return, and `stats` is safe from any thread.
+
+### Apple gamepad UI — a host menu, and About becomes a page
+
+**UP on a saved tile opens Wake / Copy link / Edit… / Forget pairing / Remove.** The desktop and
+Android consoles have had this for a while; this is the Apple port, so the three consoles are
+learned once. Wiring UP takes the whole vertical axis away from scrolling (down goes inert) — a
+horizontal carousel has no vertical travel to spend, and one meaning per direction is what makes
+the gesture learnable. **Remove arms on the first press and fires on the second**, disarming if
+focus wanders off the row: the touch grid gets a system confirmation dialog, and a thumbstick from
+across a room deserves at least as much. Edit reuses `GamepadAddHostView` seeded from the record and
+writes a **copy** back through `HostStore.update`, so the fingerprint, MACs, pins and binding the
+form never shows survive a rename; it **replaces** the menu rather than stacking on it, keeping the
+shell's "depth ≤ 1 by construction" true. A pinned profile card offers only Unpin — it is a
+shortcut, not a second host.
+
+**The start-of-stream shortcut banner is retired.** Telling someone the controls for six seconds,
+over the stream they just connected to, answers the question at the one moment nobody is asking it
+— and it put a composited overlay above the stream to do it. The words are now a catalogue rendered
+in an About page you can open, which is also its own section rather than the last row of Interface.
+Its remaining fixes: the identity card became a version line under the rows, a zero-radius clip is
+still a clip (it cropped the TV's wide icon), and the card ignored the row column.
+
+⚠ **Apple console screens read the ink they publish.** A SwiftUI screen cannot read the environment
+value it publishes in the same view — so a pale palette stayed white-on-white on Apple TV. Fixed
+across every console screen.
+
+### Console UI — Skia sized its function table to the loader, not to what we promised
+
+🛑 **On a Steam Deck the console home died on update**, and in a stream the same failure quietly
+cost the stats OSD and capture HUD.
+
+The skia-safe 0.87 → 0.99 move swapped `BackendContext::new` for `new_builder(…, None)` and
+recorded the `None` as "byte-for-byte what the removed constructor did". True of the **value**,
+false of the **behaviour**: `None` leaves Skia's `fMaxAPIVersion` at its `0` sentinel, and the newer
+Skia acts on that sentinel by falling back to **`vkEnumerateInstanceVersion()` — the loader's
+ceiling, not ours.** The presenter declares 1.3; a current Mesa answers 1.4 (1.4.321 on SteamOS
+3.7, host and inside the flatpak sandbox alike). Skia then validates a 1.4 function table against an
+instance that only promised 1.3, `vkGetDeviceProcAddr` returns null for the entry points in
+between, and `make_vulkan` hands back `None`. At 0.87 the sentinel was inert because that Skia knew
+nothing of Vulkan 1.4 — **which is why this surfaced the moment v0.28.0 landed.**
+
+`run.rs` makes an overlay that cannot init fatal for `--browse`, so the Decky panel's button and the
+gamepad-UI library shortcut both failed to open. The presenter now publishes
+`SharedDevice::api_version` — `min(what we declared, what the loader reports)` — and
+`SkiaOverlay::init` passes it instead of `None`. ⚠ `pf-presenter`'s `vk` module is
+`cfg(any(linux, windows))`, so this was never Deck-specific.
+
+### pf-vkdecode — AV1's "maximum parameters" level is not a level above the ceiling
+
+🛑 **Every AV1 session demoted to D3D11VA** with `stream level (seq_level_idx 31) above the device's
+maxLevel (AV1 Std level 23)` — on hardware decoding the stream trivially on the rung it fell
+through to.
+
+`seq_level_idx` is a 5-bit field: Annex A defines 0…23 (levels 2.0…7.3), reserves 24…30, and makes
+**31 the "maximum parameters" level — the spec's own way of saying the bitstream is not constrained
+to a level.** `StdVideoAV1Level` stops at 7.3 = 23, so 31 has no Std code point and the index-coded
+comparison that holds across 0…23 says nothing: `31 > 23` is true even of a device that decodes
+everything AV1 can name, which is what makes it useless as a capability test. We write no AV1 level
+on any host encode path, so whichever sentinel the vendor's encoder defaults to is what the client
+must accept. This is the AV1 half of the same defect fixed for H.264/H.265 in v0.28.0, which was
+left alone on the premise that no over-declaration had been seen in the field — the reporter's log
+from that same day already showed otherwise.
+
+### Client stats — the stage line is a partition again
+
+A field reader added up `host 5.4 · net 0.3 · decode 6.6 · display 1.4` against `e2e 8.1` and asked
+why the parts did not sum. Fair question: they sum **without** `decode`.
+
+The stages *are* a per-frame partition of e2e — pts →(host+net)→ received →(decode)→ decoded
+→(display)→ displayed — for as long as the `decoded` stamp is a **completion** stamp. On the
+synchronous rungs it is. On the **native-Vulkan** rung `receive_frame` returns at *submission*
+(~0.1 ms) and the stamp is taken there, so `display` is measured from submit and the GPU decode
+happens **inside** it. `host+net` and `display` already tile e2e; the `decode` figure (received →
+fence-complete) re-counts the GPU work `display` contains — two figures with one overlap, printed
+as though they tiled.
+
+On that rung `decode` now leaves the stage line and gets its own, carrying the two caveats a reader
+needs: it is **one sample per window** there, not the p50 every other figure on that line is, and it
+is already inside `display`, so adding it double-counts. The synchronous rungs are untouched.
+⚠ **Deliberately not changed:** the one-sample-per-window design. A per-frame fence wait serialises
+the decode pipeline (an APU's 19 ms decode capping a 5120×1440 stream at ~51 fps) and polling
+quantises every sample up by a frame interval. The reporting was the defect, not the sampling.
+
+### Host — two warnings that named the wrong subsystem
+
+Both fired in the same 2026-08-13 field log, and both sent an investigation somewhere innocent:
+
+- **"Client keyframe recoveries are METRONOMIC — a periodic host/display disturbance … is the
+  likely cause"**, at `period_s=2.0`, naming three host subsystems. **2.0 s is the *client's*
+  `FLUSH_COOLDOWN`.** The receive-backlog guard sheds a standing queue with a flush plus a keyframe
+  request, rate-limited to one per cooldown, so a client that cannot sustain the stream asks for a
+  keyframe at exactly that spacing for as long as it stays behind. **Perfect periodicity is the
+  signature of a fixed software cooldown, not of a physical disturbance.** The host now compares
+  against `punktfunk_core::client::FLUSH_COOLDOWN` itself rather than a copy of the number, so the
+  two cannot drift.
+- **"The audio encode thread could not keep up — captured audio was DROPPED"**, worst case
+  `dropped_chunks=11251`. Not one sample anybody wanted was lost. PipeWire negotiated a 128-frame
+  quantum, so the plane produces 48000/128 = 375 chunks/s and a 30 s window holds exactly 11250 —
+  a 100 % drop rate at `peak_db=-120.0`, digital silence. Every one of the ten warnings straddled a
+  **session boundary**, and `dropped_chunks/375` matches the seconds with *no live session* in that
+  window to within a fraction of a second. The warning no longer fires for idle seconds.
+
 ### NixOS — the plugin runner was installed, running, and reported missing
 
 🛑 **On NixOS every plugin *package* op failed with "the plugin runner isn't installed", on a box
@@ -217,6 +629,19 @@ NixOS ships only `sh` in `/bin`, so `gamelease`'s hand-off test and `pyrowave_re
 handshake-rung test failed there for reasons unrelated to the code under test. Both now resolve a
 real binary rather than assuming an FHS path.
 
+### Documentation
+
+**`docs-site/public/openapi.json` was stale again, and by the same mechanism as last release.**
+v0.28.0 fixed it once (it was five releases behind at `0.21.0`); the scanner-removal regen then
+updated `api/openapi.json` alone and it drifted a second time inside that same cycle. It has now
+drifted a third time, across the unpair-all endpoints — the docs-site copy was still stamped
+`0.27.0` and missing both collection deletes. Re-synced; the two files are byte-identical again.
+
+⚠ **The copy is a documented manual step (`cp api/openapi.json docs-site/public/openapi.json`,
+CONTRIBUTING.md) and nothing in CI enforces it.** Three drifts in two release cycles is the
+argument for gating it; until something does, **treat the copy as part of regenerating, not as a
+follow-up.**
+
 ---
 
 ## v0.28.0

Cargo.lock

@@ -1090,7 +1090,7 @@ dependencies = [
 
 [[package]]
 name = "cursor-probe"
-version = "0.28.0"
+version = "0.28.1"
 dependencies = [
  "anyhow",
  "pf-capture",
@@ -1222,7 +1222,7 @@ dependencies = [
 
 [[package]]
 name = "display-disturb"
-version = "0.28.0"
+version = "0.28.1"
 dependencies = [
  "pf-win-display",
  "windows 0.62.2 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -2343,7 +2343,7 @@ dependencies = [
 
 [[package]]
 name = "latency-probe"
-version = "0.28.0"
+version = "0.28.1"
 
 [[package]]
 name = "lazy_static"
@@ -2446,7 +2446,7 @@ dependencies = [
 
 [[package]]
 name = "libvpl-sys"
-version = "0.28.0"
+version = "0.28.1"
 dependencies = [
  "bindgen",
  "cmake",
@@ -2475,7 +2475,7 @@ checksum = "0ceec5bc11778974d1bcb055b18002eba7f4b3518b6a0081b3af5f21666da9ad"
 
 [[package]]
 name = "loss-harness"
-version = "0.28.0"
+version = "0.28.1"
 dependencies = [
  "punktfunk-core",
 ]
@@ -2967,7 +2967,7 @@ checksum = "9b4f627cb1b25917193a259e49bdad08f671f8d9708acfd5fe0a8c1455d87220"
 
 [[package]]
 name = "pf-bitstream"
-version = "0.28.0"
+version = "0.28.1"
 dependencies = [
  "cros-codecs",
  "tracing",
@@ -2975,7 +2975,7 @@ dependencies = [
 
 [[package]]
 name = "pf-capture"
-version = "0.28.0"
+version = "0.28.1"
 dependencies = [
  "anyhow",
  "ashpd",
@@ -2996,7 +2996,7 @@ dependencies = [
 
 [[package]]
 name = "pf-client-core"
-version = "0.28.0"
+version = "0.28.1"
 dependencies = [
  "anyhow",
  "ash",
@@ -3031,7 +3031,7 @@ dependencies = [
 
 [[package]]
 name = "pf-clipboard"
-version = "0.28.0"
+version = "0.28.1"
 dependencies = [
  "anyhow",
  "ashpd",
@@ -3049,7 +3049,7 @@ dependencies = [
 
 [[package]]
 name = "pf-console-ui"
-version = "0.28.0"
+version = "0.28.1"
 dependencies = [
  "anyhow",
  "ash",
@@ -3071,7 +3071,7 @@ dependencies = [
 
 [[package]]
 name = "pf-dxvadec"
-version = "0.28.0"
+version = "0.28.1"
 dependencies = [
  "cros-codecs",
  "pf-bitstream",
@@ -3081,7 +3081,7 @@ dependencies = [
 
 [[package]]
 name = "pf-encode"
-version = "0.28.0"
+version = "0.28.1"
 dependencies = [
  "anyhow",
  "ash",
@@ -3107,7 +3107,7 @@ dependencies = [
 
 [[package]]
 name = "pf-frame"
-version = "0.28.0"
+version = "0.28.1"
 dependencies = [
  "anyhow",
  "libc",
@@ -3119,7 +3119,7 @@ dependencies = [
 
 [[package]]
 name = "pf-gpu"
-version = "0.28.0"
+version = "0.28.1"
 dependencies = [
  "anyhow",
  "pf-host-config",
@@ -3133,11 +3133,11 @@ dependencies = [
 
 [[package]]
 name = "pf-host-config"
-version = "0.28.0"
+version = "0.28.1"
 
 [[package]]
 name = "pf-inject"
-version = "0.28.0"
+version = "0.28.1"
 dependencies = [
  "anyhow",
  "ashpd",
@@ -3166,14 +3166,14 @@ dependencies = [
 
 [[package]]
 name = "pf-paths"
-version = "0.28.0"
+version = "0.28.1"
 dependencies = [
  "tracing",
 ]
 
 [[package]]
 name = "pf-presenter"
-version = "0.28.0"
+version = "0.28.1"
 dependencies = [
  "anyhow",
  "ash",
@@ -3188,7 +3188,7 @@ dependencies = [
 
 [[package]]
 name = "pf-update"
-version = "0.28.0"
+version = "0.28.1"
 dependencies = [
  "serde",
  "serde_json",
@@ -3196,7 +3196,7 @@ dependencies = [
 
 [[package]]
 name = "pf-update-check"
-version = "0.28.0"
+version = "0.28.1"
 dependencies = [
  "anyhow",
  "aws-lc-rs",
@@ -3208,7 +3208,7 @@ dependencies = [
 
 [[package]]
 name = "pf-vaadec"
-version = "0.28.0"
+version = "0.28.1"
 dependencies = [
  "cros-codecs",
  "pf-bitstream",
@@ -3217,7 +3217,7 @@ dependencies = [
 
 [[package]]
 name = "pf-vdisplay"
-version = "0.28.0"
+version = "0.28.1"
 dependencies = [
  "anyhow",
  "ashpd",
@@ -3250,7 +3250,7 @@ dependencies = [
 
 [[package]]
 name = "pf-vkdecode"
-version = "0.28.0"
+version = "0.28.1"
 dependencies = [
  "ash",
  "cros-codecs",
@@ -3261,7 +3261,7 @@ dependencies = [
 
 [[package]]
 name = "pf-win-display"
-version = "0.28.0"
+version = "0.28.1"
 dependencies = [
  "pf-paths",
  "punktfunk-core",
@@ -3272,7 +3272,7 @@ dependencies = [
 
 [[package]]
 name = "pf-zerocopy"
-version = "0.28.0"
+version = "0.28.1"
 dependencies = [
  "anyhow",
  "ash",
@@ -3484,7 +3484,7 @@ dependencies = [
 
 [[package]]
 name = "punktfunk-cli"
-version = "0.28.0"
+version = "0.28.1"
 dependencies = [
  "pf-client-core",
  "punktfunk-core",
@@ -3494,7 +3494,7 @@ dependencies = [
 
 [[package]]
 name = "punktfunk-client-android"
-version = "0.28.0"
+version = "0.28.1"
 dependencies = [
  "android_logger",
  "jni",
@@ -3512,7 +3512,7 @@ dependencies = [
 
 [[package]]
 name = "punktfunk-client-linux"
-version = "0.28.0"
+version = "0.28.1"
 dependencies = [
  "anyhow",
  "async-channel",
@@ -3529,7 +3529,7 @@ dependencies = [
 
 [[package]]
 name = "punktfunk-client-session"
-version = "0.28.0"
+version = "0.28.1"
 dependencies = [
  "pf-client-core",
  "pf-console-ui",
@@ -3543,7 +3543,7 @@ dependencies = [
 
 [[package]]
 name = "punktfunk-client-windows"
-version = "0.28.0"
+version = "0.28.1"
 dependencies = [
  "async-channel",
  "mdns-sd",
@@ -3561,7 +3561,7 @@ dependencies = [
 
 [[package]]
 name = "punktfunk-core"
-version = "0.28.0"
+version = "0.28.1"
 dependencies = [
  "aes-gcm",
  "cbindgen",
@@ -3593,7 +3593,7 @@ dependencies = [
 
 [[package]]
 name = "punktfunk-encode-worker"
-version = "0.28.0"
+version = "0.28.1"
 dependencies = [
  "pf-encode",
  "tracing",
@@ -3602,7 +3602,7 @@ dependencies = [
 
 [[package]]
 name = "punktfunk-host"
-version = "0.28.0"
+version = "0.28.1"
 dependencies = [
  "aes",
  "aes-gcm",
@@ -3672,7 +3672,7 @@ dependencies = [
 
 [[package]]
 name = "punktfunk-probe"
-version = "0.28.0"
+version = "0.28.1"
 dependencies = [
  "anyhow",
  "mdns-sd",
@@ -3686,7 +3686,7 @@ dependencies = [
 
 [[package]]
 name = "punktfunk-tray"
-version = "0.28.0"
+version = "0.28.1"
 dependencies = [
  "anyhow",
  "ksni",
@@ -3709,7 +3709,7 @@ checksum = "d55d956fa96f5ec02be2e13af0e20391a5aa83d6a074e3ad368959d0fab299ea"
 
 [[package]]
 name = "pyrowave-sys"
-version = "0.28.0"
+version = "0.28.1"
 dependencies = [
  "bindgen",
  "cmake",

Cargo.toml

@@ -65,7 +65,7 @@ exclude = [
 ndk = { path = "clients/android/native/vendor/ndk" }
 
 [workspace.package]
-version = "0.28.0"
+version = "0.28.1"
 edition = "2024"
 rust-version = "1.85"
 license = "MIT OR Apache-2.0"

clients/apple/Sources/PunktfunkKit/Audio/AudioDeviceWatcher.swift

@@ -32,8 +32,11 @@ final class AudioDeviceWatcher {
     /// posts one last change as it is torn down, and other AVAudioEngines in the process are not
     /// ours to restart.
     private let isOurs: (AnyObject?) -> Bool
-    /// Delivered on the main queue.
-    private let onChange: (Reason) -> Void
+    /// Delivered on the main queue. The second argument is the engine that posted the change
+    /// (`.engineConfiguration` only; nil for the HAL listener) — the owner needs the OBJECT, not
+    /// just the reason, because an engine that is RUNNING when the notification lands is one the
+    /// owner already restarted: acting on that echo is how a rebuild loop starts.
+    private let onChange: (Reason, AnyObject?) -> Void
 
     private let lock = NSLock()
     private var configObserver: NSObjectProtocol?
@@ -41,7 +44,7 @@ final class AudioDeviceWatcher {
     private var defaultOutputListener: AudioObjectPropertyListenerBlock?
     #endif
 
-    init(isOurs: @escaping (AnyObject?) -> Bool, onChange: @escaping (Reason) -> Void) {
+    init(isOurs: @escaping (AnyObject?) -> Bool, onChange: @escaping (Reason, AnyObject?) -> Void) {
         self.isOurs = isOurs
         self.onChange = onChange
     }
@@ -63,7 +66,7 @@ final class AudioDeviceWatcher {
             let posted = note.object as AnyObject?
             DispatchQueue.main.async {
                 guard let self, self.isOurs(posted) else { return }
-                self.onChange(.engineConfiguration)
+                self.onChange(.engineConfiguration, posted)
             }
         }
         lock.lock()
@@ -77,7 +80,8 @@ final class AudioDeviceWatcher {
         // (the voice-processing engine, which is the DEFAULT macOS configuration and which no Mac
         // here can even initialize). The HAL is told either way.
         let block: AudioObjectPropertyListenerBlock = { [weak self] _, _ in
-            self?.onChange(.defaultOutputDevice) // on the main queue — registered against it below
+            // On the main queue — registered against it below. No engine posted this, so nil.
+            self?.onChange(.defaultOutputDevice, nil)
         }
         var address = Self.defaultOutputAddress()
         let status = AudioObjectAddPropertyListenerBlock(

clients/apple/Sources/PunktfunkKit/Audio/AudioDevices.swift

@@ -42,7 +42,10 @@ public enum AudioDevices {
         return channelCount(id, scope: kAudioObjectPropertyScopeInput)
     }
 
-    private static func defaultInputDevice() -> AudioDeviceID? {
+    /// The device the system is currently capturing from — the key `SessionAudio`'s
+    /// voice-processing gate latches a start failure against (the failure is a property of the
+    /// input device, so a new device earns a fresh attempt).
+    static func defaultInputDevice() -> AudioDeviceID? {
         systemDevice(kAudioHardwarePropertyDefaultInputDevice)
     }
 

clients/apple/Sources/PunktfunkKit/Audio/AudioRebuildPolicy.swift

@@ -0,0 +1,89 @@
+// The two policy decisions of the device-change recovery, extracted where a unit test can reach
+// them. Both exist because of one field incident (2026-08-14, Mac Studio): the voice-processing
+// engine could not start on a 6-channel input device, every rebuild re-tried it, and the failed
+// attempt's HAL churn (VPIO builds and tears down an aggregate device) re-stopped the fallback
+// engines — which posted the configuration change that scheduled the next rebuild. A ~2.5 s
+// metronome of audio gaps, forever, with each rebuild also stalling the main thread (where macOS
+// input capture lives), so the stream's INPUT cut out on the same beat. The session-side wiring
+// lives in `SessionAudio`; the decisions live here because the loop shipped precisely because
+// they could not be tested without a mic and a session.
+
+#if os(macOS)
+import CoreAudio
+#endif
+import Foundation
+
+#if os(macOS)
+/// Should a rebuild try the combined (voice-processing) topology again?
+///
+/// A VPIO start failure is a property of the INPUT DEVICE (its channel count and format), not of
+/// the moment: retrying it on the same device fails the same way, and the attempt is not free —
+/// engaging and abandoning the voice processor churns the HAL hard enough to stop the healthy
+/// fallback engines. So a failure latches until the default input actually changes; a new device
+/// earns exactly one fresh attempt (it may well support VPIO), and its own failure latches again.
+struct CombinedTopologyGate {
+    private var failed = false
+    /// The default input device the failure was observed on — nil is a real value here ("failed
+    /// with no resolvable input device"), which is why `failed` is tracked separately.
+    private var failedInput: AudioDeviceID?
+
+    /// The combined topology failed with `input` as the default input device.
+    mutating func noteFailure(input: AudioDeviceID?) {
+        failed = true
+        failedInput = input
+    }
+
+    /// True when the combined topology is worth attempting with `input` as the default input
+    /// device. A device change clears the latch — the answer is about the CURRENT hardware, and
+    /// coming back to a device that failed before earns a fresh attempt too (the failure may have
+    /// been the mid-transition kind, and one attempt per device change cannot loop).
+    mutating func shouldTry(input: AudioDeviceID?) -> Bool {
+        guard failed else { return true }
+        guard input == failedInput else {
+            failed = false
+            failedInput = nil
+            return true
+        }
+        return false
+    }
+}
+#endif
+
+/// The delay before the next engine rebuild — the base debounce/floor behaviour, plus an
+/// escalating floor when rebuilds CHAIN (each one retriggered by its predecessor's own fallout).
+///
+/// One device switch produces one rebuild: its trigger burst is coalesced upstream, so the next
+/// trigger normally arrives minutes later and gets the base floor. A trigger that arrives hard on
+/// the heels of the last rebuild, again and again, is a rebuild answering itself — and since the
+/// recovery cannot always identify its own echo, the backstop is to keep answering but at a
+/// doubling floor, so an unforeseen feedback shape costs one audio blip per half-minute instead
+/// of a metronome. A quiet stretch resets the ladder to full responsiveness.
+struct RebuildBackoff {
+    /// Let the burst of triggers from one switch land before rebuilding.
+    static let debounce: TimeInterval = 0.15
+    /// Floor between two rebuilds.
+    static let floor: TimeInterval = 0.5
+    /// The escalated floor's cap: looping recoveries settle at one attempt per this interval.
+    static let floorCap: TimeInterval = 30
+    /// A trigger this long after the last rebuild is unrelated to it — the chain resets.
+    static let chainWindow: TimeInterval = 10
+
+    /// Consecutive rebuilds whose trigger arrived within `chainWindow` of the previous rebuild.
+    private(set) var chain = 0
+    private var lastRebuildAt: TimeInterval = -.infinity
+
+    /// The delay to schedule the next rebuild with, for a trigger arriving at `now`
+    /// (`systemUptime`). Mutates the chain accounting: call once per SCHEDULED rebuild, not per
+    /// coalesced trigger.
+    mutating func delay(now: TimeInterval) -> TimeInterval {
+        let since = now - lastRebuildAt
+        chain = since < Self.chainWindow ? chain + 1 : 0
+        let floor = min(Self.floor * pow(2, Double(min(chain, 6))), Self.floorCap)
+        return max(Self.debounce, floor - since)
+    }
+
+    /// The rebuild actually ran at `now` — the reference the next trigger's `delay` measures from.
+    mutating func noteRebuild(at now: TimeInterval) {
+        lastRebuildAt = now
+    }
+}

clients/apple/Sources/PunktfunkKit/Audio/SessionAudio.swift

@@ -63,15 +63,24 @@ public final class SessionAudio {
     private var micMuted = false
     /// The playback jitter ring — created by whichever engine starts playback first and KEPT
     /// across an engine rebuild (the permission-grant upgrade in `startEngines` swaps engines,
-    /// not the ring, so the drain thread never has to be re-pointed). Main-thread confined,
-    /// like every start path.
+    /// not the ring, so the drain thread never has to be re-pointed). Guarded by `stateLock`:
+    /// the start paths run on `engineQueue`, while `stats` reads from the main thread.
     private var ring: AudioRing?
+    /// Every engine build, start, stop and rebuild runs here, serially — and NOT on the main
+    /// thread. macOS captures and sends input from the main thread, so the seconds a
+    /// voice-processing start can take (~1.9 s measured in the 2026-08-14 field loop) would
+    /// freeze the stream's input for exactly that long — the recovery must never make the main
+    /// thread wait on the audio server. The main queue keeps only the trigger bookkeeping
+    /// (debounce, backoff, retry ladder), which is cheap by construction.
+    private let engineQueue = DispatchQueue(
+        label: "io.unom.punktfunk.audio.engines", qos: .userInitiated)
     /// The video plane's end-to-end meter (capture→on-glass), if the owner wired one — the
     /// reference the A/V sync loop steers the ring against. `nil` leaves the loop inert and the
     /// ring exactly as it was before sync existed, which is also what the stage-1 fallback
     /// presenter gets: it decodes and presents inside the layer with no per-frame stamp, so it can
-    /// offer no reference, and a loop with no reference must not invent one. Main-thread confined,
-    /// like `ring`; the meter itself is internally locked and read from the drain thread.
+    /// offer no reference, and a loop with no reference must not invent one. Written ONCE in
+    /// `start()` before anything is dispatched (the queue hop orders it for `startDrain`); the
+    /// meter itself is internally locked and read from the drain thread.
     private var videoLatency: LatencyMeter?
     #if !os(macOS)
     /// AVAudioSession `setCategory`/`setActive` are synchronous and block on the audio server, so
@@ -99,7 +108,8 @@ public final class SessionAudio {
     // MARK: - Device changes (see `installDeviceChangeRecovery`)
 
     /// What `start()` was asked for, so a rebuild can put back the SAME topology the session was
-    /// started with. Main-thread confined, like the start paths that read it.
+    /// started with. Guarded by `stateLock` (written on the caller's thread, read when a rebuild
+    /// fires on the main queue).
     private var startConfig: StartConfig?
     private struct StartConfig {
         let speakerUID: String
@@ -110,20 +120,23 @@ public final class SessionAudio {
     }
     /// Watches the hardware for us (see `AudioDeviceWatcher`). Guarded by `stateLock`.
     private var deviceWatcher: AudioDeviceWatcher?
-    /// Whether the engines have been built at least once. Distinguishes "not started yet" (iOS
-    /// starts asynchronously) from "started and dead", which is what the recovery may act on.
-    /// Main-thread confined.
+    /// Whether the engines have been built at least once. Distinguishes "not started yet" (every
+    /// platform starts asynchronously now) from "started and dead", which is what the recovery
+    /// may act on. Guarded by `stateLock` (set on `engineQueue`, read on the main queue).
     private var enginesAttempted = false
     /// A rebuild is already on the main queue — one device switch produces a burst of triggers
     /// and they must collapse into one restart. Main-thread confined.
     private var rebuildQueued = false
-    /// `systemUptime` of the last rebuild, so a device that renegotiates in a loop cannot spin
-    /// the session. Main-thread confined.
-    private var lastRebuildAt: TimeInterval = 0
-    /// Let the burst of triggers from one switch land before rebuilding.
-    private static let rebuildDebounce: TimeInterval = 0.15
-    /// Floor between two rebuilds.
-    private static let rebuildFloor: TimeInterval = 0.5
+    /// Debounce/floor for the next rebuild, with an escalating floor when rebuilds chain (each
+    /// retriggered by its predecessor — see `RebuildBackoff`). Main-thread confined.
+    private var rebuildBackoff = RebuildBackoff()
+    #if os(macOS)
+    /// Latches a voice-processing start failure per input device, so a rebuild never re-attempts
+    /// a topology that deterministically fails — the retry is what turned one failure into a
+    /// rebuild loop (see `CombinedTopologyGate` and the note on `installDeviceChangeRecovery`).
+    /// `engineQueue`-confined, like the start paths that consult and feed it.
+    private var combinedGate = CombinedTopologyGate()
+    #endif
     /// Retries when a rebuild's `start()` loses the race with a device that is still going away
     /// (0.3 s, 0.6 s, 1.2 s). A failed rebuild leaves no engine to post the next notification,
     /// so this ladder — and, on macOS, the HAL listener — is all that stands between a mistimed
@@ -151,11 +164,12 @@ public final class SessionAudio {
     }
 
     /// Start playback (and, if enabled+authorized, the mic uplink). Empty UIDs = system default
-    /// device; on iOS the UIDs are ignored entirely (routes are AVAudioSession-managed). On macOS
-    /// the engines start synchronously on the caller's (main) thread. On iOS/tvOS start() is
-    /// ASYNCHRONOUS: it activates the AVAudioSession off the main thread, then starts the engines on
-    /// a later main-queue hop (gated by `!flag.isStopped`) — so playback is live shortly after, not
-    /// on return. The mic may start later still if the permission prompt is pending.
+    /// device; on iOS the UIDs are ignored entirely (routes are AVAudioSession-managed).
+    /// ASYNCHRONOUS on every platform: the engines start on `engineQueue` (iOS/tvOS activate the
+    /// AVAudioSession off the main thread first), gated by `!flag.isStopped` — so playback is
+    /// live shortly after, not on return. An engine start can block on the audio server for
+    /// seconds, and the caller's (main) thread is where macOS input capture lives — it must
+    /// never wait. The mic may start later still if the permission prompt is pending.
     /// `echoCancel` picks the engine topology — see the header note and `wantsCombined`.
     ///
     /// `videoLatency` is the session's END-TO-END latency meter (capture→on-glass). Pass it to arm
@@ -166,26 +180,33 @@ public final class SessionAudio {
         speakerUID: String, micUID: String, micChannel: Int, micEnabled: Bool, echoCancel: Bool,
         videoLatency: LatencyMeter? = nil
     ) {
-        self.videoLatency = videoLatency
+        self.videoLatency = videoLatency // before any dispatch below — startDrain reads it
         // Before any engine exists: the recovery watches the hardware, not the engines, and the
         // config it rebuilds from has to be recorded whether or not this start succeeds.
+        stateLock.lock()
         startConfig = StartConfig(
             speakerUID: speakerUID, micUID: micUID, micChannel: micChannel,
             micEnabled: micEnabled, echoCancel: echoCancel)
+        stateLock.unlock()
         installDeviceChangeRecovery(micEnabled: micEnabled)
         #if os(macOS)
-        // No AVAudioSession on macOS — start the engines directly (caller's thread, as before).
-        startEngines(
-            speakerUID: speakerUID, micUID: micUID, micChannel: micChannel,
-            micEnabled: micEnabled, echoCancel: echoCancel)
+        // No AVAudioSession on macOS — but the engines start on `engineQueue`, never the
+        // caller's (main) thread: a voice-processing start can block on the audio server for
+        // seconds, and the main thread is where input capture lives.
+        engineQueue.async { [weak self] in
+            guard let self, !self.flag.isStopped else { return }
+            self.startEngines(
+                speakerUID: speakerUID, micUID: micUID, micChannel: micChannel,
+                micEnabled: micEnabled, echoCancel: echoCancel)
+        }
         #else
         // Configure + activate the session OFF the main thread (it blocks on the audio server),
-        // then start the engines back on the main thread once it's active — engine routing/format
+        // then start the engines on `engineQueue` once it's active — engine routing/format
         // depend on the active session. A stop() racing in between is caught by the flag guard.
         Self.sessionQueue.async { [weak self] in
             guard let self else { return }
             self.activateAudioSession(micEnabled: micEnabled)
-            DispatchQueue.main.async { [weak self] in
+            self.engineQueue.async { [weak self] in
                 guard let self, !self.flag.isStopped else { return }
                 self.startEngines(
                     speakerUID: speakerUID, micUID: micUID, micChannel: micChannel,
@@ -342,12 +363,15 @@ public final class SessionAudio {
     #endif
 
     /// Build + start the engines — combined (voice-processed) or split, per `wantsCombined` —
-    /// with the mic uplink only when enabled + authorized. Main thread (engine setup); on
-    /// iOS/tvOS the session is already active by the time this runs.
+    /// with the mic uplink only when enabled + authorized. Runs on `engineQueue` (a start can
+    /// block on the audio server for seconds — never the main thread); on iOS/tvOS the session
+    /// is already active by the time this runs.
     private func startEngines(
         speakerUID: String, micUID: String, micChannel: Int, micEnabled: Bool, echoCancel: Bool
     ) {
+        stateLock.lock()
         enginesAttempted = true // even if every path below fails — see `reviveStoppedEngines`
+        stateLock.unlock()
         #if os(tvOS)
         // No app-accessible microphone input on tvOS — playback only.
         startPlayback(speakerUID: speakerUID)
@@ -356,9 +380,25 @@ public final class SessionAudio {
             startPlayback(speakerUID: speakerUID)
             return
         }
+        #if os(macOS)
+        // A rebuild must not re-attempt a voice-processing start that already failed on this
+        // input device: the failure repeats, and the failed attempt's HAL churn stops the healthy
+        // fallback engines — the 2026-08-14 rebuild loop (see `CombinedTopologyGate`).
+        var combined = wantsCombined(
+            speakerUID: speakerUID, micUID: micUID, micChannel: micChannel,
+            echoCancel: echoCancel)
+        if combined, !combinedGate.shouldTry(input: AudioDevices.defaultInputDevice()) {
+            log.info("""
+                voice processing already failed on this input device — split engines, no echo \
+                cancellation
+                """)
+            combined = false
+        }
+        #else
         let combined = wantsCombined(
             speakerUID: speakerUID, micUID: micUID, micChannel: micChannel,
             echoCancel: echoCancel)
+        #endif
         switch AVCaptureDevice.authorizationStatus(for: .audio) {
         case .authorized:
             if combined {
@@ -374,7 +414,8 @@ public final class SessionAudio {
             // drain thread carry over — see `makePlaybackChain`).
             startPlayback(speakerUID: speakerUID)
             AVCaptureDevice.requestAccess(for: .audio) { [weak self] granted in
-                DispatchQueue.main.async {
+                guard let self else { return }
+                self.engineQueue.async { [weak self] in
                     guard let self, granted, !self.flag.isStopped else { return }
                     if combined {
                         self.stateLock.lock()
@@ -513,6 +554,17 @@ public final class SessionAudio {
     ///  - the route-change and media-services-reset notifications, iOS/tvOS, where the session and
     ///    not the device is what moves.
     ///
+    /// And three defenses keep the recovery from ANSWERING ITSELF — a rebuild is not a silent
+    /// act (a voice-processing start builds and tears down HAL aggregates, and every fresh engine
+    /// renegotiates its IO), so its own fallout can retrigger it. The 2026-08-14 field loop was
+    /// exactly that: VPIO failed on a 6-channel mic, every rebuild re-tried it, and the failure's
+    /// churn stopped the fallback engines — audio and (via the main thread) INPUT cutting out
+    /// every ~2.5 s for the whole session. The defenses: a configuration change from an engine
+    /// that is RUNNING is a rebuild's echo and is ignored (`hardwareMoved`); a VPIO failure is
+    /// latched per input device and never re-attempted on it (`CombinedTopologyGate`); and
+    /// rebuilds that chain anyway back off exponentially instead of metronoming
+    /// (`RebuildBackoff`).
+    ///
     /// `micEnabled` only decides whether the mic-bearing session observers are worth installing.
     /// Main thread.
     private func installDeviceChangeRecovery(micEnabled: Bool) {
@@ -523,7 +575,7 @@ public final class SessionAudio {
 
         let watcher = AudioDeviceWatcher(
             isOurs: { [weak self] posted in self?.ownsEngine(posted) ?? false },
-            onChange: { [weak self] reason in self?.hardwareMoved(reason) })
+            onChange: { [weak self] reason, posted in self?.hardwareMoved(reason, posted: posted) })
         stateLock.lock()
         deviceWatcher = watcher
         stateLock.unlock()
@@ -549,10 +601,17 @@ public final class SessionAudio {
     /// question — is playback still where it should be — but they answer it differently: an engine
     /// that told us it stopped is definitive, while the default device moving might not concern us
     /// at all.
-    private func hardwareMoved(_ reason: AudioDeviceWatcher.Reason) {
+    private func hardwareMoved(_ reason: AudioDeviceWatcher.Reason, posted: AnyObject?) {
         guard !flag.isStopped else { return }
         switch reason {
         case .engineConfiguration:
+            // The engine stops itself BEFORE posting this — so an engine that is RUNNING when the
+            // notification lands on the main queue is one a rebuild already replaced or restarted:
+            // the notification is the rebuild's own echo, and answering it is how the recovery
+            // loops. A change that stops the engine again after this posts again, and the HAL
+            // backstop checks placement independently, so ignoring a live engine's echo can never
+            // strand a stopped one.
+            if let engine = posted as? AVAudioEngine, engine.isRunning { return }
             scheduleEngineRebuild(reason: reason.rawValue)
         case .defaultOutputDevice:
             #if os(macOS)
@@ -572,7 +631,10 @@ public final class SessionAudio {
     /// output device at the moment it connected — and leaving it silent for good. On iOS the same
     /// flag keeps this from racing the asynchronous start, where no engine yet is normal.
     private func reviveStoppedEngines(_ reason: String) {
-        guard !flag.isStopped, enginesAttempted, !playbackIsLive else { return }
+        stateLock.lock()
+        let attempted = enginesAttempted
+        stateLock.unlock()
+        guard !flag.isStopped, attempted, !playbackIsLive else { return }
         scheduleEngineRebuild(reason: "playback is stopped and \(reason)")
     }
 
@@ -594,15 +656,43 @@ public final class SessionAudio {
     private func scheduleEngineRebuild(reason: String) {
         guard !rebuildQueued else { return }
         rebuildQueued = true
-        let since = ProcessInfo.processInfo.systemUptime - lastRebuildAt
-        let delay = max(Self.rebuildDebounce, Self.rebuildFloor - since)
-        log.info("\(reason) — restarting the audio engines in \(Int(delay * 1000)) ms")
+        let delay = rebuildBackoff.delay(now: ProcessInfo.processInfo.systemUptime)
+        if rebuildBackoff.chain >= 2 {
+            // Each rebuild is retriggering the next — a feedback shape the echo guard and the
+            // topology gate did not identify. Keep answering (a real recovery must not be
+            // abandoned), but say what is happening: this line repeating IS the diagnosis.
+            log.warning("""
+                audio engine rebuilds are chaining (\(self.rebuildBackoff.chain) in a row — \
+                \(reason)); backing off \(Int(delay * 1000)) ms
+                """)
+        } else {
+            log.info("\(reason) — restarting the audio engines in \(Int(delay * 1000)) ms")
+        }
         DispatchQueue.main.asyncAfter(deadline: .now() + delay) { [weak self] in
-            self?.rebuildEngines(attempt: 0)
+            self?.rebuildFire(attempt: 0)
+        }
+    }
+
+    /// The scheduled rebuild came due (main queue): close out the bookkeeping and hand the
+    /// actual engine work to `engineQueue` — the teardown + start can block on the audio server
+    /// for seconds, and the main thread is where macOS captures and sends the stream's input.
+    /// A trigger arriving while the work is in flight schedules a fresh rebuild rather than
+    /// being swallowed; `engineQueue` is serial, so the two never interleave.
+    private func rebuildFire(attempt: Int) {
+        rebuildQueued = false
+        guard !flag.isStopped else { return }
+        stateLock.lock()
+        let config = startConfig
+        stateLock.unlock()
+        guard let config else { return }
+        rebuildBackoff.noteRebuild(at: ProcessInfo.processInfo.systemUptime)
+        engineQueue.async { [weak self] in
+            self?.performRebuild(config: config, attempt: attempt)
         }
     }
 
     /// Put back the topology this session was started with, on whatever hardware is there now.
+    /// Runs on `engineQueue`.
     ///
     /// A full rebuild rather than a `start()` on the stopped engine, because the mic side has to
     /// follow too: `installMicTap` reads the input's live format, and the voice processor
@@ -610,10 +700,8 @@ public final class SessionAudio {
     /// across (`makePlaybackChain` reuses it, `startDrain` is idempotent), so the drain thread
     /// keeps decoding right through the switch and its overflow policy has already dropped
     /// everything that went stale while the engine was down.
-    private func rebuildEngines(attempt: Int) {
-        rebuildQueued = false
-        guard !flag.isStopped, let config = startConfig else { return }
-        lastRebuildAt = ProcessInfo.processInfo.systemUptime
+    private func performRebuild(config: StartConfig, attempt: Int) {
+        guard !flag.isStopped else { return }
         tearDownEngines()
         startEngines(
             speakerUID: config.speakerUID, micUID: config.micUID, micChannel: config.micChannel,
@@ -626,6 +714,18 @@ public final class SessionAudio {
             log.info("audio engines restarted on the current device")
             return
         }
+        DispatchQueue.main.async { [weak self] in
+            self?.rebuildFailed(attempt: attempt)
+        }
+    }
+
+    /// A rebuild's playback did not come back (main queue) — walk the retry ladder. Retries
+    /// when a rebuild's `start()` loses the race with a device that is still going away
+    /// (0.3 s, 0.6 s, 1.2 s): a failed rebuild leaves no engine to post the next notification,
+    /// so this ladder — and, on macOS, the HAL listener — is all that stands between a mistimed
+    /// switch and a silent session.
+    private func rebuildFailed(attempt: Int) {
+        guard !flag.isStopped else { return }
         guard attempt < Self.rebuildAttempts else {
             #if os(macOS)
             log.error("""
@@ -637,10 +737,11 @@ public final class SessionAudio {
             #endif
             return
         }
+        guard !rebuildQueued else { return } // a fresh trigger already queued a full rebuild
         rebuildQueued = true // holds off a trigger that would only race this ladder
-        let delay = Self.rebuildDebounce * Double(1 << (attempt + 1))
+        let delay = RebuildBackoff.debounce * Double(1 << (attempt + 1))
         DispatchQueue.main.asyncAfter(deadline: .now() + delay) { [weak self] in
-            self?.rebuildEngines(attempt: attempt + 1)
+            self?.rebuildFire(attempt: attempt + 1)
         }
     }
 
@@ -786,9 +887,13 @@ public final class SessionAudio {
         public let avOffsetMS: Int
     }
 
-    /// A snapshot of `Stats`, or nil before playback starts. Main thread (`ring` is main-confined;
-    /// the ring's own numbers are taken under its lock, so they describe one instant).
+    /// A snapshot of `Stats`, or nil before playback starts. Safe from any thread (the handle is
+    /// taken under `stateLock`; the ring's own numbers are taken under its lock, so they
+    /// describe one instant).
     public var stats: Stats? {
+        stateLock.lock()
+        let ring = self.ring
+        stateLock.unlock()
         guard let s = ring?.stats else { return nil }
         return Stats(bufferMS: s.bufferedMS, avOffsetMS: s.avOffsetMS)
     }
@@ -813,7 +918,7 @@ public final class SessionAudio {
     /// The playback jitter ring + the source node draining it — shared by the plain playback
     /// engine and the combined voice-processing engine, and REUSED across an engine rebuild
     /// (same session, same ring: the drain thread keeps writing right through the swap). nil
-    /// when the host's channel layout can't be expressed (already logged). Main thread.
+    /// when the host's channel layout can't be expressed (already logged). Runs on `engineQueue`.
     private func makePlaybackChain()
         -> (ring: AudioRing, source: AVAudioSourceNode, format: AVAudioFormat)?
     {
@@ -823,8 +928,10 @@ public final class SessionAudio {
         // 1 s interleaved capacity, scaled by the channel count. The de-jitter depth itself is
         // the ring's own business now (`AudioRing.targetMS`, mirroring `JitterTuning::COREAUDIO`)
         // rather than a prefill passed in here.
+        stateLock.lock()
         let ring = self.ring ?? AudioRing(capacity: 48_000 * channels, channels: channels)
         self.ring = ring
+        stateLock.unlock()
 
         // Engine-native deinterleaved float; the render block deinterleaves from the ring. Surround
         // uses an explicit wire-order channel layout; the mixer downmixes to the output device when
@@ -983,6 +1090,17 @@ public final class SessionAudio {
     // MARK: - Mic (mic → host)
 
     #if !os(tvOS)
+    /// The combined topology failed to come up. On macOS, latch the input device it failed on so
+    /// a rebuild goes straight to the split topology instead of re-running the failure — the
+    /// failed attempt is what churns the HAL and retriggers the recovery (see
+    /// `CombinedTopologyGate`). On iOS routes are session-managed and a VPIO failure is the
+    /// transient route-transition kind, so nothing is latched there.
+    private func noteCombinedFailure() {
+        #if os(macOS)
+        combinedGate.noteFailure(input: AudioDevices.defaultInputDevice())
+        #endif
+    }
+
     /// One engine, both directions: engage the system voice processor on the shared IO unit
     /// (AEC + noise suppression + AGC), hang the playback source off its render side and the
     /// mic tap off its capture side. Every failure falls back to a WORKING configuration —
@@ -1001,6 +1119,7 @@ public final class SessionAudio {
                 voice processing unavailable (\(error.localizedDescription)) — separate \
                 engines, no echo cancellation
                 """)
+            noteCombinedFailure()
             startPlayback(speakerUID: speakerUID)
             startCapture(micUID: micUID, micChannel: micChannel)
             return
@@ -1054,6 +1173,7 @@ public final class SessionAudio {
             // processor won't engage at all, already does exactly this; this arm used to give up
             // on the mic instead, which is how a whole session could go silent uplink-only.)
             engine.stop()
+            noteCombinedFailure()
             startPlayback(speakerUID: speakerUID)
             startCapture(micUID: micUID, micChannel: micChannel)
             return
@@ -1064,6 +1184,7 @@ public final class SessionAudio {
             log.error("combined engine failed to start: \(error.localizedDescription)")
             engine.inputNode.removeTap(onBus: 0)
             engine.stop()
+            noteCombinedFailure()
             // Same rule: a working mic without echo cancellation beats no mic at all.
             startPlayback(speakerUID: speakerUID)
             startCapture(micUID: micUID, micChannel: micChannel)

clients/apple/Tests/PunktfunkKitTests/AudioDeviceWatcherTests.swift

@@ -32,7 +32,7 @@ final class AudioDeviceWatcherTests: XCTestCase {
         let engine = AVAudioEngine()
         var reasons: [AudioDeviceWatcher.Reason] = []
         let watcher = AudioDeviceWatcher(
-            isOurs: { $0 === engine }, onChange: { reasons.append($0) })
+            isOurs: { $0 === engine }, onChange: { reason, _ in reasons.append(reason) })
         watcher.start()
         defer { watcher.stop() }
 
@@ -51,7 +51,7 @@ final class AudioDeviceWatcherTests: XCTestCase {
         let stranger = AVAudioEngine()
         var reasons: [AudioDeviceWatcher.Reason] = []
         let watcher = AudioDeviceWatcher(
-            isOurs: { $0 === ours }, onChange: { reasons.append($0) })
+            isOurs: { $0 === ours }, onChange: { reason, _ in reasons.append(reason) })
         watcher.start()
         defer { watcher.stop() }
 
@@ -66,7 +66,7 @@ final class AudioDeviceWatcherTests: XCTestCase {
         let engine = AVAudioEngine()
         var reasons: [AudioDeviceWatcher.Reason] = []
         let watcher = AudioDeviceWatcher(
-            isOurs: { $0 === engine }, onChange: { reasons.append($0) })
+            isOurs: { $0 === engine }, onChange: { reason, _ in reasons.append(reason) })
         watcher.start()
         watcher.stop()
 
@@ -93,7 +93,7 @@ final class AudioDeviceWatcherTests: XCTestCase {
         }
 
         var reasons: [AudioDeviceWatcher.Reason] = []
-        let watcher = AudioDeviceWatcher(isOurs: { _ in false }, onChange: { reasons.append($0) })
+        let watcher = AudioDeviceWatcher(isOurs: { _ in false }, onChange: { reason, _ in reasons.append(reason) })
         watcher.start()
         defer {
             _ = Self.setDefaultOutput(original)

clients/apple/Tests/PunktfunkKitTests/AudioRebuildPolicyTests.swift

@@ -0,0 +1,110 @@
+// The two decisions that ended the 2026-08-14 rebuild loop, driven with a synthetic clock.
+//
+// The loop's shape, for the plant-the-defect cases below: the voice-processing engine fails to
+// start (~1.9 s spent trying), the fallback comes up, and its own HAL fallout retriggers the
+// recovery ~0.6 s later — forever. Restore either defect (retry the failed topology, or keep the
+// flat 0.5 s floor) and the session pays an audio gap every ~2.5 s for as long as it lives.
+
+import XCTest
+
+@testable import PunktfunkKit
+
+final class AudioRebuildPolicyTests: XCTestCase {
+    // MARK: - RebuildBackoff
+
+    /// The first trigger of a session keeps the old behaviour: the burst-coalescing debounce.
+    func testFirstTriggerWaitsOnlyTheDebounce() {
+        var backoff = RebuildBackoff()
+        XCTAssertEqual(backoff.delay(now: 1000), RebuildBackoff.debounce)
+    }
+
+    /// One rebuild, then quiet: the next real device switch minutes later is answered at full
+    /// responsiveness — the ladder must never make a HEALTHY recovery sluggish.
+    func testAnIsolatedSwitchLongAfterTheLastRebuildResetsTheChain() {
+        var backoff = RebuildBackoff()
+        _ = backoff.delay(now: 1000)
+        backoff.noteRebuild(at: 1000.2)
+        // Chained once (a second switch soon after — legitimate, e.g. AirPods out then back in).
+        _ = backoff.delay(now: 1001)
+        backoff.noteRebuild(at: 1002)
+        // Minutes of quiet, then a fresh switch: base debounce again, chain forgotten.
+        XCTAssertEqual(backoff.delay(now: 1300), RebuildBackoff.debounce)
+        XCTAssertEqual(backoff.chain, 0)
+    }
+
+    /// THE FIELD LOOP, against the real constants: a trigger 0.6 s after every rebuild, ten
+    /// minutes long. The flat 0.5 s floor produced a rebuild every ~2.5 s — ~240 audio gaps.
+    /// The ladder must cut that by an order of magnitude and settle at the floor cap.
+    func testAChainedLoopBacksOffToTheFloorCap() {
+        var backoff = RebuildBackoff()
+        var now: TimeInterval = 0
+        var rebuilds = 0
+        var lastDelay: TimeInterval = 0
+        let end: TimeInterval = 600
+        while now < end {
+            lastDelay = backoff.delay(now: now)
+            now += lastDelay // the scheduled rebuild fires...
+            backoff.noteRebuild(at: now)
+            rebuilds += 1
+            now += 0.6 // ...and its fallout retriggers the recovery 0.6 s later.
+        }
+        XCTAssertEqual(
+            lastDelay, RebuildBackoff.floorCap - 0.6, accuracy: 0.01,
+            "a persistent loop should settle at one rebuild per floorCap")
+        XCTAssertLessThanOrEqual(
+            rebuilds, 30,
+            "\(rebuilds) rebuilds in 10 min — the ladder is not escalating (the shipped flat "
+                + "floor produced ~240)")
+        // And the loop's END must restore responsiveness: quiet, then a real switch.
+        XCTAssertEqual(backoff.delay(now: now + 120), RebuildBackoff.debounce)
+    }
+
+    /// The ladder's exponent is clamped — a loop that runs for hours must neither overflow nor
+    /// push the interval past the cap.
+    func testTheFloorNeverExceedsTheCap() {
+        var backoff = RebuildBackoff()
+        var now: TimeInterval = 0
+        for _ in 0..<1000 {
+            let delay = backoff.delay(now: now)
+            XCTAssertLessThanOrEqual(delay, RebuildBackoff.floorCap)
+            now += delay
+            backoff.noteRebuild(at: now)
+            now += 0.1
+        }
+    }
+
+    #if os(macOS)
+    // MARK: - CombinedTopologyGate
+
+    /// The loop's fuel: re-attempting the voice-processing start that just failed. Same input
+    /// device ⇒ never again.
+    func testAFailureLatchesForTheDeviceItFailedOn() {
+        var gate = CombinedTopologyGate()
+        XCTAssertTrue(gate.shouldTry(input: 42), "an unfailed gate must allow the attempt")
+        gate.noteFailure(input: 42)
+        XCTAssertFalse(gate.shouldTry(input: 42))
+        XCTAssertFalse(gate.shouldTry(input: 42), "the latch must hold across rebuilds")
+    }
+
+    /// The failure is a property of the DEVICE: a different default input earns a fresh attempt,
+    /// and its own failure latches again — one attempt per device change can never loop.
+    func testADifferentInputDeviceEarnsOneFreshAttempt() {
+        var gate = CombinedTopologyGate()
+        gate.noteFailure(input: 42)
+        XCTAssertTrue(gate.shouldTry(input: 7))
+        gate.noteFailure(input: 7)
+        XCTAssertFalse(gate.shouldTry(input: 7))
+        // Back to the first device: the earlier failure may have been mid-transition — one fresh
+        // attempt again, not a permanent ban.
+        XCTAssertTrue(gate.shouldTry(input: 42))
+    }
+
+    /// "No resolvable input device" is a real failure key too, distinct from "never failed".
+    func testFailingWithNoInputDeviceLatchesForNoInputDevice() {
+        var gate = CombinedTopologyGate()
+        gate.noteFailure(input: nil)
+        XCTAssertFalse(gate.shouldTry(input: nil))
+        XCTAssertTrue(gate.shouldTry(input: 42), "a device appearing is a device change")
+    }
+    #endif
+}

crates/pf-host-config/src/lib.rs

@@ -214,6 +214,15 @@ pub struct HostConfig {
     /// showing the wrong monitor is worse than showing none). Linux-only today; see
     /// `design/per-monitor-portal-capture.md`.
     pub capture_monitor: Option<String>,
+    /// `PUNKTFUNK_PORTAL_CURSOR_MODE` — `auto` (default) · `hidden` · `embedded` · `metadata`.
+    /// Pin the ScreenCast cursor mode the Linux portal backends PREFER, instead of the one the
+    /// session negotiates (`metadata` when the client draws the pointer itself, `embedded`
+    /// otherwise). The pin is a preference, not a command: it still runs through
+    /// `portal_cursor::pick`, so it can never ask a backend for a mode the backend does not
+    /// advertise — that closes the session rather than degrading, which is the failure this knob
+    /// sits next to. Exists for the backend that advertises a mode it implements badly, where
+    /// negotiation has nothing to go on; `embedded` is the safe answer there.
+    pub portal_cursor_mode: Option<String>,
     /// `PUNKTFUNK_COMPOSITOR` — explicit compositor override (operator/CI/test). NOT the runtime-detected
     /// session — this one is a constant operator knob; `apply_session_env` never writes it.
     pub compositor: Option<String>,
@@ -401,6 +410,12 @@ impl HostConfig {
             capture_monitor: val("PUNKTFUNK_CAPTURE_MONITOR")
                 .map(|s| s.trim().to_string())
                 .filter(|s| !s.is_empty()),
+            // Same emptied-to-None rule: a bare `PUNKTFUNK_PORTAL_CURSOR_MODE=` left in a host.env
+            // means "not set", not an unrecognised value to warn about. The spellings are parsed
+            // (and warned about) at the use site, `pf-vdisplay`'s `portal_cursor::want`.
+            portal_cursor_mode: val("PUNKTFUNK_PORTAL_CURSOR_MODE")
+                .map(|s| s.trim().to_string())
+                .filter(|s| !s.is_empty()),
             compositor: val("PUNKTFUNK_COMPOSITOR"),
             gamepad: val("PUNKTFUNK_GAMEPAD"),
             vdisplay: val("PUNKTFUNK_VDISPLAY"),

crates/pf-vdisplay/src/lib.rs

@@ -824,6 +824,15 @@ pub mod admission;
 #[path = "vdisplay/linux/portal_config.rs"]
 mod portal_config;
 
+/// Which ScreenCast cursor mode to REQUEST — negotiated against `AvailableCursorModes` instead of
+/// hardcoded, because a mode the backend does not advertise closes the session outright.
+///
+/// Declared unconditionally for the same reason as `portal_config` above: the ladder is pure
+/// integer work whose tests are the only place its behaviour is observable without a compositor,
+/// so they should run on every platform's CI rather than only where the callers compile.
+#[path = "vdisplay/linux/portal_cursor.rs"]
+mod portal_cursor;
+
 #[cfg(target_os = "linux")]
 #[path = "vdisplay/linux/hyprland.rs"]
 mod hyprland;

crates/pf-vdisplay/src/vdisplay/linux/hyprland.rs

@@ -115,12 +115,21 @@ fn output_owner_pid(name: &str) -> Option<u32> {
 /// The Hyprland virtual-display driver. Stateless — each [`create`](VirtualDisplay::create) adds one
 /// named headless output and spins up a portal thread owning the cast on it.
 pub struct HyprlandDisplay {
-    /// Out-of-band cursor request (`set_hw_cursor`, the negotiated cursor channel): portal
+    /// Out-of-band cursor request (`set_hw_cursor`, the negotiated cursor channel): PREFER portal
     /// `CursorMode::Metadata` — shapes/positions ride `SPA_META_Cursor` for the channel + the
-    /// composite blend. Off (every non-channel session): `Embedded` — the compositor paints the
-    /// pointer into frames, zero host-side cursor work (the pre-channel default this backend
-    /// always had). ⚠️ Metadata is UNTESTED on-glass for this backend (Phase B wired it so the
-    /// channel isn't silently dead here; KWin/Mutter are the validated legs).
+    /// composite blend. Off (every non-channel session): prefer `Embedded` — the compositor paints
+    /// the pointer into frames, zero host-side cursor work (the pre-channel default this backend
+    /// always had).
+    ///
+    /// Both are only a PREFERENCE: [`crate::portal_cursor`] settles it against what xdph actually
+    /// advertises, because requesting an unadvertised mode makes xdg-desktop-portal fail the call.
+    /// This used to be asserted instead, which is exactly how a cursor-forward session here became
+    /// a black client.
+    ///
+    /// ⚠️ On current xdph the metadata arm is UNREACHABLE, not merely untested: measured on .21
+    /// 2026-08-14 (Hyprland 0.56.2, xdph 1.4.1) `AvailableCursorModes` = 3 — `Hidden|Embedded`
+    /// only. Every session on this backend therefore resolves to `Embedded` today; KWin/Mutter
+    /// remain the legs where the metadata channel is actually exercised.
     hw_cursor: bool,
 }
 
@@ -788,13 +797,7 @@ fn portal_thread(
     stop: Arc<AtomicBool>,
     hw_cursor: bool,
 ) {
-    // Portal cursor mode per the session's channel negotiation (see the struct doc).
-    let cursor_mode = if hw_cursor {
-        CursorMode::Metadata
-    } else {
-        CursorMode::Embedded
-    };
-    use ashpd::desktop::screencast::{CursorMode, Screencast, SelectSourcesOptions, SourceType};
+    use ashpd::desktop::screencast::{Screencast, SelectSourcesOptions, SourceType};
     use ashpd::desktop::PersistMode;
     use ashpd::enumflags2::BitFlags;
 
@@ -818,6 +821,14 @@ fn portal_thread(
             let proxy = Screencast::new().await.context(
                 "connect ScreenCast portal (is xdg-desktop-portal running with the hyprland backend/xdph?)",
             )?;
+            // NEGOTIATED against what xdph advertises, never asserted from `hw_cursor` alone: a
+            // cursor mode the backend does not offer does not degrade — xdg-desktop-portal's
+            // FRONTEND fails the call ("Unavailable cursor mode %x") before xdph sees it.
+            // MEASURED on .21 2026-08-14, Hyprland 0.56.2 + xdph 1.4.1 (both current):
+            // `AvailableCursorModes` = 3 (Hidden|Embedded) — metadata is NOT offered. So the old
+            // hardcode killed EVERY cursor-forward session here, on today's packages, not just on
+            // old installs: `unavailable cursor mode 4`, "pipeline build failed", black client.
+            let cursor_mode = crate::portal_cursor::negotiate(&proxy, hw_cursor, "xdph").await;
             let session = proxy
                 .create_session(Default::default())
                 .await

crates/pf-vdisplay/src/vdisplay/linux/portal_cursor.rs

@@ -0,0 +1,376 @@
+//! Which ScreenCast cursor mode to ASK the portal for — negotiated against what the backend
+//! advertises, rather than asserted.
+//!
+//! The portal spec is unforgiving here: `SelectSources` with a cursor mode that is absent from
+//! `AvailableCursorModes` does not quietly degrade — **xdg-desktop-portal itself rejects the call**
+//! (`"Unavailable cursor mode %x"`, an `INVALID_ARGUMENT` from the FRONTEND, which validates the
+//! request against the backend's advertised bitfield before the backend ever sees it). Both
+//! wlr-family backends used to hardcode `Metadata` whenever the session had negotiated the cursor
+//! channel, so every cursor-forward session died at `select_sources` — `unavailable cursor mode 4`
+//! (4 being `Metadata`'s bit) and a client left on a black screen behind "pipeline build failed".
+//! Field report 2026-08-14.
+//!
+//! ⚠️ This is NOT a stale-portal problem, and not Hyprland-specific. MEASURED on .21 2026-08-14 on
+//! fully current packages — Hyprland **0.56.2**, xdg-desktop-portal-hyprland **1.4.1**,
+//! xdg-desktop-portal **1.22.1** — with a live session and xdph attached (`[screencopy] init
+//! successful`): `AvailableCursorModes` reads **3** (`Hidden|Embedded`) on both the backend impl
+//! interface and the frontend. **Metadata is simply not offered by xdph today.** xdpw is the same
+//! story from the other end: its `screencast.c` refuses `METADATA` outright. So the hardcode broke
+//! every cursor-forward session on the entire wlr family, on current software — not only on old
+//! installs. (xdph 1.4.1 would itself fall back — its binary carries
+//! `"[screencopy] unsupported cursor_mode {}, fallback to {}"` — but it never gets the chance,
+//! because the frontend fails the call first.)
+//!
+//! `pf-capture`'s own portal path has always negotiated (`portal::choose_cursor_mode`) — this is
+//! that ladder, restated in the crate that owns the virtual-display backends. pf-vdisplay must not
+//! depend on pf-capture (see this crate's Cargo.toml: "never on capture/inject or the
+//! orchestrator"), so the two copies are deliberate; keep the ladders in step.
+//!
+//! Declared unconditionally although only the Linux backends call it: the ladder is pure integer
+//! work, and its tests are the whole point of the module — this is a decision that leaves no trace
+//! anyone can check without a compositor in front of them — so they run on every platform's CI
+//! rather than on the one leg that compiles `mod hyprland`.
+
+/// A ScreenCast cursor mode, valued as the portal's own wire bits — which is what a backend prints
+/// when it rejects one, so `Metadata`'s `4` is literally the number in the field report.
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub(crate) enum Mode {
+    /// No pointer in the cast at all.
+    Hidden = 1,
+    /// The compositor paints the pointer into the frames it hands us.
+    Embedded = 2,
+    /// The pointer rides `SPA_META_Cursor` metadata beside the frames: the compositor keeps its
+    /// cheap hardware cursor plane, and the consumer either composites the shape itself or
+    /// forwards it to a client that draws its own.
+    Metadata = 4,
+}
+
+impl Mode {
+    /// The portal's bit for this mode.
+    pub(crate) const fn bit(self) -> u32 {
+        self as u32
+    }
+
+    /// The spelling used in logs and in `PUNKTFUNK_PORTAL_CURSOR_MODE`.
+    pub(crate) const fn name(self) -> &'static str {
+        match self {
+            Mode::Hidden => "hidden",
+            Mode::Embedded => "embedded",
+            Mode::Metadata => "metadata",
+        }
+    }
+
+    /// What to ask for instead, best first, when this mode is not advertised.
+    const fn fallbacks(self) -> [Mode; 2] {
+        match self {
+            // The session wanted out-of-band shapes and cannot have them. `Embedded` still puts a
+            // pointer on the client's screen (the compositor's, burnt in) — and because no
+            // `SPA_META_Cursor` then arrives, the host feeds the cursor channel nothing and a
+            // cursor-forward client draws nothing of its own, so this is one pointer, not two.
+            // `Hidden` is last: it streams a desktop nobody can point at.
+            Mode::Metadata => [Mode::Embedded, Mode::Hidden],
+            // Embedded wanted but not offered. Metadata still beats Hidden: the CPU capture path
+            // composites `SPA_META_Cursor` inline, so part of the matrix keeps a pointer.
+            Mode::Embedded => [Mode::Metadata, Mode::Hidden],
+            // A deliberate request for no pointer that the backend will not honour. Either
+            // remaining mode shows one; prefer the cheap burnt-in pointer over metadata nothing on
+            // this path is set up to draw.
+            Mode::Hidden => [Mode::Embedded, Mode::Metadata],
+        }
+    }
+}
+
+/// The outcome of the ladder: what to request, and what the session actually wanted if those
+/// differ (the caller logs the gap — a silently downgraded cursor is how this class of bug hides).
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub(crate) struct Choice {
+    /// The mode to put in `SelectSources`. Advertised, unless the backend advertised nothing.
+    pub(crate) mode: Mode,
+    /// Set only when `mode` is a downgrade: the mode the session asked for and could not have.
+    pub(crate) wanted: Option<Mode>,
+}
+
+/// Pick the cursor mode to request, given the backend's `AvailableCursorModes` bitfield.
+///
+/// Never returns a mode outside `advertised` unless `advertised` names none we know — see the tail
+/// comment, which is the one case with no right answer.
+pub(crate) fn pick(advertised: u32, want: Mode) -> Choice {
+    if advertised & want.bit() != 0 {
+        return Choice {
+            mode: want,
+            wanted: None,
+        };
+    }
+    for alt in want.fallbacks() {
+        if advertised & alt.bit() != 0 {
+            return Choice {
+                mode: alt,
+                wanted: Some(want),
+            };
+        }
+    }
+    // The backend advertised no mode this build knows — 0, or only bits from a spec revision newer
+    // than us. Every request is then a coin flip against a session-closing rejection; `Hidden` is
+    // both the most universally implemented and the only one that cannot end up drawing two
+    // pointers. The caller warns: whatever this backend is doing, we are guessing.
+    Choice {
+        mode: Mode::Hidden,
+        wanted: Some(want),
+    }
+}
+
+/// A parsed `PUNKTFUNK_PORTAL_CURSOR_MODE`.
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub(crate) enum Pin {
+    /// Unset or `auto` — the session's own negotiation decides.
+    Auto,
+    /// Prefer this mode instead of what the session negotiated. Still runs the ladder, so a pin
+    /// can never re-create the session-killing request this module exists to prevent.
+    Mode(Mode),
+    /// Set to something we do not recognise. Treated as `Auto`, but the caller says so out loud —
+    /// a typo'd escape hatch that silently does nothing is worse than no escape hatch.
+    Unrecognised,
+}
+
+/// Parse the `PUNKTFUNK_PORTAL_CURSOR_MODE` value.
+pub(crate) fn parse_pin(raw: &str) -> Pin {
+    match raw.trim().to_ascii_lowercase().as_str() {
+        "" | "auto" => Pin::Auto,
+        "hidden" | "none" => Pin::Mode(Mode::Hidden),
+        "embedded" | "composited" => Pin::Mode(Mode::Embedded),
+        "metadata" | "meta" => Pin::Mode(Mode::Metadata),
+        _ => Pin::Unrecognised,
+    }
+}
+
+/// The mode this session wants before the backend gets a say: `Metadata` when the cursor channel
+/// was negotiated (`set_hw_cursor` — the client draws the pointer, so the compositor must not burn
+/// it in), `Embedded` otherwise. `PUNKTFUNK_PORTAL_CURSOR_MODE` overrides both.
+///
+/// `backend` names the portal implementation for the log line only (`xdph`, `xdpw`).
+#[cfg_attr(not(target_os = "linux"), allow(dead_code))]
+pub(crate) fn want(hw_cursor: bool, backend: &str) -> Mode {
+    let negotiated = if hw_cursor {
+        Mode::Metadata
+    } else {
+        Mode::Embedded
+    };
+    let raw = match pf_host_config::config().portal_cursor_mode.as_deref() {
+        Some(raw) => raw,
+        None => return negotiated,
+    };
+    match parse_pin(raw) {
+        Pin::Auto => negotiated,
+        Pin::Mode(pinned) => {
+            tracing::info!(
+                backend,
+                pinned = pinned.name(),
+                negotiated = negotiated.name(),
+                "ScreenCast: cursor mode pinned by PUNKTFUNK_PORTAL_CURSOR_MODE"
+            );
+            pinned
+        }
+        Pin::Unrecognised => {
+            tracing::warn!(
+                backend,
+                value = raw,
+                negotiated = negotiated.name(),
+                "ScreenCast: unrecognised PUNKTFUNK_PORTAL_CURSOR_MODE (want auto|hidden|embedded|\
+                 metadata) — ignoring"
+            );
+            negotiated
+        }
+    }
+}
+
+#[cfg(target_os = "linux")]
+impl Mode {
+    fn to_ashpd(self) -> ashpd::desktop::screencast::CursorMode {
+        use ashpd::desktop::screencast::CursorMode;
+        match self {
+            Mode::Hidden => CursorMode::Hidden,
+            Mode::Embedded => CursorMode::Embedded,
+            Mode::Metadata => CursorMode::Metadata,
+        }
+    }
+}
+
+/// Ask the portal what it supports, run the ladder, and hand back the mode to put in
+/// `SelectSources`. Infallible by construction: a backend we cannot interrogate gets `Embedded`,
+/// the mode that predates the property and that every implementation has always had.
+#[cfg(target_os = "linux")]
+pub(crate) async fn negotiate(
+    proxy: &ashpd::desktop::screencast::Screencast,
+    hw_cursor: bool,
+    backend: &str,
+) -> ashpd::desktop::screencast::CursorMode {
+    let want = want(hw_cursor, backend);
+    let advertised = match proxy.available_cursor_modes().await {
+        Ok(avail) => avail.bits(),
+        Err(e) => {
+            // `AvailableCursorModes` is a versioned property (ScreenCast v2); a portal too old to
+            // publish it is also too old to have metadata, and `Embedded` is what this backend
+            // requested for its whole life before the cursor channel existed.
+            tracing::warn!(
+                backend,
+                error = %e,
+                "ScreenCast: AvailableCursorModes query failed — requesting Embedded cursor"
+            );
+            return Mode::Embedded.to_ashpd();
+        }
+    };
+    let choice = pick(advertised, want);
+    match choice.wanted {
+        None => tracing::info!(
+            backend,
+            advertised = format_args!("{advertised:#05b}"),
+            mode = choice.mode.name(),
+            "ScreenCast: cursor mode negotiated"
+        ),
+        // The downgrade path — and the one that used to be a dead session. Loud, because a stream
+        // whose pointer quietly changed hands is exactly what nobody thinks to check.
+        Some(wanted) => tracing::warn!(
+            backend,
+            advertised = format_args!("{advertised:#05b}"),
+            wanted = wanted.name(),
+            mode = choice.mode.name(),
+            "ScreenCast: requested cursor mode is not advertised by this portal — downgrading \
+             (requesting it anyway would close the session)"
+        ),
+    }
+    choice.mode.to_ashpd()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    /// The portal's wire values. These are ABI — a backend rejecting our request prints the
+    /// number, and `4` is the one in the field report that started this module.
+    #[test]
+    fn mode_bits_are_the_portal_wire_values() {
+        assert_eq!(Mode::Hidden.bit(), 1);
+        assert_eq!(Mode::Embedded.bit(), 2);
+        assert_eq!(Mode::Metadata.bit(), 4);
+    }
+
+    /// Our `Mode` is a restatement of ashpd's `CursorMode`, whose bits enumflags2 assigns from
+    /// declaration order — so a reordering upstream would silently repoint every mode. Pin it
+    /// where ashpd is actually compiled.
+    #[cfg(target_os = "linux")]
+    #[test]
+    fn mode_bits_match_ashpd() {
+        use ashpd::desktop::screencast::CursorMode;
+        use ashpd::enumflags2::BitFlags;
+        for m in [Mode::Hidden, Mode::Embedded, Mode::Metadata] {
+            assert_eq!(
+                BitFlags::from_flag(m.to_ashpd()).bits(),
+                m.bit(),
+                "{} drifted from ashpd",
+                m.name()
+            );
+        }
+        assert_eq!(BitFlags::from_flag(CursorMode::Metadata).bits(), 4);
+    }
+
+    /// THE REGRESSION, with the real number: `3` is what xdph actually advertises — measured on
+    /// .21 2026-08-14 against a live Hyprland 0.56.2 + xdph 1.4.1, both current. A cursor-forward
+    /// session wants metadata; asking for it made xdg-desktop-portal fail the call, and the client
+    /// got a black screen behind "pipeline build failed" / "unavailable cursor mode 4".
+    #[test]
+    fn metadata_wanted_but_unadvertised_downgrades_to_embedded() {
+        // Exactly the bitfield the portal reported on glass.
+        assert_eq!(Mode::Hidden.bit() | Mode::Embedded.bit(), 3);
+        let c = pick(3, Mode::Metadata);
+        assert_eq!(c.mode, Mode::Embedded);
+        assert_eq!(c.wanted, Some(Mode::Metadata));
+    }
+
+    /// The same portal, a session with no cursor channel: already asking for what exists, so the
+    /// fix must not perturb it.
+    #[test]
+    fn embedded_wanted_and_advertised_is_untouched() {
+        let c = pick(Mode::Hidden.bit() | Mode::Embedded.bit(), Mode::Embedded);
+        assert_eq!(c.mode, Mode::Embedded);
+        assert_eq!(c.wanted, None);
+    }
+
+    /// A portal that does support metadata (KWin, Mutter, xdph ≥ #366) still gets it — the point
+    /// is to stop asserting, not to stop using it.
+    #[test]
+    fn metadata_is_used_where_advertised() {
+        let all = Mode::Hidden.bit() | Mode::Embedded.bit() | Mode::Metadata.bit();
+        let c = pick(all, Mode::Metadata);
+        assert_eq!(c.mode, Mode::Metadata);
+        assert_eq!(c.wanted, None);
+    }
+
+    /// Embedded wanted, only metadata offered: the CPU capture path composites it, so a pointer
+    /// survives. (Mirrors `pf-capture`'s ladder.)
+    #[test]
+    fn embedded_unadvertised_falls_to_metadata_not_hidden() {
+        let c = pick(Mode::Hidden.bit() | Mode::Metadata.bit(), Mode::Embedded);
+        assert_eq!(c.mode, Mode::Metadata);
+        assert_eq!(c.wanted, Some(Mode::Embedded));
+    }
+
+    /// A backend offering only `Hidden`: a cursorless stream beats a closed session.
+    #[test]
+    fn hidden_only_backend_yields_hidden() {
+        let c = pick(Mode::Hidden.bit(), Mode::Metadata);
+        assert_eq!(c.mode, Mode::Hidden);
+        assert_eq!(c.wanted, Some(Mode::Metadata));
+    }
+
+    /// Advertises nothing we know — no right answer, but it must still be a legal enum and flagged
+    /// as a downgrade so the warn fires.
+    #[test]
+    fn unknown_advertisement_guesses_hidden_and_reports_a_downgrade() {
+        for advertised in [0, 0b1000_0000] {
+            let c = pick(advertised, Mode::Metadata);
+            assert_eq!(c.mode, Mode::Hidden);
+            assert_eq!(c.wanted, Some(Mode::Metadata));
+        }
+    }
+
+    /// Whatever the ladder returns must be a mode the backend named — the invariant the old
+    /// hardcode broke. Exhaustive over every advertisement × every want.
+    #[test]
+    fn never_requests_an_unadvertised_mode() {
+        let modes = [Mode::Hidden, Mode::Embedded, Mode::Metadata];
+        for advertised in 1u32..=0b111 {
+            for want in modes {
+                let c = pick(advertised, want);
+                assert!(
+                    advertised & c.mode.bit() != 0,
+                    "picked {} from advertised {advertised:#05b} (want {})",
+                    c.mode.name(),
+                    want.name()
+                );
+                // A downgrade is reported exactly when one happened.
+                assert_eq!(c.wanted.is_some(), c.mode != want);
+            }
+        }
+    }
+
+    #[test]
+    fn pin_parses_the_spellings_we_document() {
+        assert_eq!(parse_pin(""), Pin::Auto);
+        assert_eq!(parse_pin("auto"), Pin::Auto);
+        assert_eq!(parse_pin(" AUTO "), Pin::Auto);
+        assert_eq!(parse_pin("embedded"), Pin::Mode(Mode::Embedded));
+        assert_eq!(parse_pin("Embedded"), Pin::Mode(Mode::Embedded));
+        assert_eq!(parse_pin("metadata"), Pin::Mode(Mode::Metadata));
+        assert_eq!(parse_pin("hidden"), Pin::Mode(Mode::Hidden));
+        assert_eq!(parse_pin("2"), Pin::Unrecognised);
+        assert_eq!(parse_pin("yes"), Pin::Unrecognised);
+    }
+
+    /// The hatch pins a PREFERENCE, not the request: pinning metadata at a portal without it must
+    /// still come out embedded rather than re-closing the session.
+    #[test]
+    fn a_pin_still_runs_the_ladder() {
+        let c = pick(Mode::Hidden.bit() | Mode::Embedded.bit(), Mode::Metadata);
+        assert_eq!(c.mode, Mode::Embedded);
+    }
+}

crates/pf-vdisplay/src/vdisplay/linux/wlroots.rs

@@ -55,12 +55,17 @@ fn chooser_cmd() -> String {
 /// The wlroots/Sway virtual-display driver. Stateless — each [`create`](VirtualDisplay::create)
 /// adds one headless output and spins up a portal thread owning the cast on it.
 pub struct WlrootsDisplay {
-    /// Out-of-band cursor request (`set_hw_cursor`, the negotiated cursor channel): portal
+    /// Out-of-band cursor request (`set_hw_cursor`, the negotiated cursor channel): PREFER portal
     /// `CursorMode::Metadata` — shapes/positions ride `SPA_META_Cursor` for the channel + the
-    /// composite blend. Off (every non-channel session): `Embedded` — the compositor paints the
-    /// pointer into frames, zero host-side cursor work (the pre-channel default this backend
-    /// always had). ⚠️ Metadata is UNTESTED on-glass for this backend (Phase B wired it so the
-    /// channel isn't silently dead here; KWin/Mutter are the validated legs).
+    /// composite blend. Off (every non-channel session): prefer `Embedded` — the compositor paints
+    /// the pointer into frames, zero host-side cursor work (the pre-channel default this backend
+    /// always had).
+    ///
+    /// Both are only a PREFERENCE: [`crate::portal_cursor`] settles it against what xdpw actually
+    /// advertises, because requesting an unadvertised mode closes the session outright. xdpw
+    /// refuses metadata by construction (see the portal thread), so on this backend the channel can
+    /// never be served out-of-band: it now degrades to `Embedded` and streams, where it used to
+    /// cancel the cast and hand the client a black screen.
     hw_cursor: bool,
 }
 
@@ -512,13 +517,7 @@ fn portal_thread(
     stop: Arc<AtomicBool>,
     hw_cursor: bool,
 ) {
-    // Portal cursor mode per the session's channel negotiation (see the struct doc).
-    let cursor_mode = if hw_cursor {
-        CursorMode::Metadata
-    } else {
-        CursorMode::Embedded
-    };
-    use ashpd::desktop::screencast::{CursorMode, Screencast, SelectSourcesOptions, SourceType};
+    use ashpd::desktop::screencast::{Screencast, SelectSourcesOptions, SourceType};
     use ashpd::desktop::PersistMode;
     use ashpd::enumflags2::BitFlags;
 
@@ -542,6 +541,14 @@ fn portal_thread(
             let proxy = Screencast::new().await.context(
                 "connect ScreenCast portal (is xdg-desktop-portal running with the wlr backend?)",
             )?;
+            // NEGOTIATED against what xdpw advertises, never asserted from `hw_cursor` alone — see
+            // the xdph copy in `hyprland.rs` for the incident. xdpw is the sharper case: its
+            // screencast.c refuses the mode outright —
+            //     if (sess->screencast_data.cursor_mode & METADATA) {
+            //         logprint(ERROR, "dbus: unsupported cursor mode requested, cancelling");
+            // — so EVERY cursor-forward session on this backend asked for a mode that cancelled the
+            // cast. Different wording from xdph's "unavailable cursor mode 4", same dead session.
+            let cursor_mode = crate::portal_cursor::negotiate(&proxy, hw_cursor, "xdpw").await;
             let session = proxy
                 .create_session(Default::default())
                 .await

docs-site/content/docs/configuration.md

@@ -115,6 +115,7 @@ See your desktop page ([KDE](/docs/kde), [GNOME](/docs/gnome)) for when to set t
 |---|---|---|
 | `PUNKTFUNK_KWIN_VIRTUAL_PRIMARY` | `1` | Make the streamed per-session output the sole desktop so plasmashell + windows render on it (not on the headless bootstrap output). Set by the KDE appliance `host.env`. Superseded by the console's **Topology** setting. |
 | `PUNKTFUNK_MUTTER_VIRTUAL_PRIMARY` | `1` | GNOME/Mutter equivalent of the above. |
+| `PUNKTFUNK_PORTAL_CURSOR_MODE` | `auto` *(default)* · `embedded` · `metadata` · `hidden` | **Hyprland / wlroots only, and a troubleshooting knob** — which ScreenCast cursor mode the host asks the portal for. Unset, the host asks for `metadata` when the client draws the pointer itself and `embedded` otherwise, then settles that against the modes your portal advertises; it never requests one your portal lacks. Set `embedded` if the pointer misbehaves on a portal that *claims* metadata support but implements it poorly — that is the one case the automatic negotiation cannot detect. A pin is still only a preference: it is checked against the advertised modes like any other. |
 
 ## Session recovery (Linux)
 

docs-site/content/docs/hyprland.md

@@ -84,6 +84,31 @@ and fails the session with a clear error rather than streaming a blank surface.
 capture the Hyprland log (`hyprctl` instance dir → `hyprland.log`) and check your GPU's GBM support;
 running Hyprland as a real session (not nested) is the supported configuration.
 
+## Troubleshooting: black client + "unavailable cursor mode 4"
+
+A black client, `pipeline build failed` in the host log, and **`unavailable cursor mode 4`** from
+xdph are one failure, not three.
+
+`4` is the ScreenCast portal's *metadata* cursor mode, which the host prefers when the client draws
+the pointer locally (desktop mouse mode). xdg-desktop-portal-hyprland **does not offer that mode** —
+on a current stack (Hyprland 0.56.2, xdph 1.4.1) its `AvailableCursorModes` is `3`, meaning hidden
+and embedded only. Asking for a mode the backend does not advertise is not a soft failure:
+`xdg-desktop-portal` rejects the call outright, so the cast died during setup and the client had
+nothing to show.
+
+Updating xdph does **not** fix this — the mode is absent on current versions, not just old ones.
+Hosts from this release check what your portal advertises and use an embedded cursor instead, so the
+session streams. If you are on an older host, switch the client to **game mouse mode**: that stops
+it asking for the metadata cursor at all.
+
+If the pointer misbehaves on an xdph that *does* advertise metadata support, pin the mode:
+
+```sh
+PUNKTFUNK_PORTAL_CURSOR_MODE=embedded
+```
+
+See [Configuration](/docs/configuration#compositor-specific-linux).
+
 ## Permission system
 
 Hyprland's permission system (`ecosystem.enforce_permissions`, 0.49+, **off by default**) can deny

docs-site/content/docs/sway.md

@@ -82,6 +82,20 @@ For how long the virtual output lives, and extend-vs-exclusive topology, see
   Then `systemctl --user restart xdg-desktop-portal`. On a box with only xdpw installed there is
   nothing to choose between, so you can skip this.
 
+## Troubleshooting: black client + "unsupported cursor mode requested"
+
+A black client with `pipeline build failed` in the host log and **`dbus: unsupported cursor mode
+requested, cancelling`** from xdpw is one failure, not two.
+
+xdpw refuses the ScreenCast *metadata* cursor mode and cancels the cast, and the portal spec makes
+that fatal rather than a fallback. Hosts before this release asked for it whenever the client drew
+the pointer itself (desktop mouse mode), so those sessions never produced a frame. Hosts from this
+release check what xdpw advertises first and use an embedded cursor instead, so the session streams.
+
+On an older host, switch the client to **game mouse mode** — it stops asking for the metadata cursor
+and the stream comes up. The same failure on Hyprland reads `unavailable cursor mode 4`; see
+[Hyprland](/docs/hyprland).
+
 ## Start the host
 
 With the backend selected, start the host from **inside your Sway session**:

docs-site/public/openapi.json

@@ -10,7 +10,7 @@
       "name": "MIT OR Apache-2.0",
       "identifier": "MIT OR Apache-2.0"
     },
-    "version": "0.27.0"
+    "version": "0.28.0"
   },
   "paths": {
     "/api/v1/clients": {
@@ -45,6 +45,36 @@
             }
           }
         }
+      },
+      "delete": {
+        "tags": [
+          "clients"
+        ],
+        "summary": "Unpair every client",
+        "description": "The collection form of [`unpair_client`]: empties the pairing store in ONE persisted write,\ncarrying the same revocation guarantees across the whole set. A LIVE GameStream session is\nended (its owning certificate is necessarily one of those just removed), and the ENet control\nport (UDP 47999) closes, because no pairing is left to hold it open.\n\nIdempotent, and so a 200 rather than the single unpair's 204/404 pair: \"unpair everything\" is\nsatisfied by an already-empty store, and the operator still wants to know whether that meant\nthree devices or none.",
+        "operationId": "unpairAllClients",
+        "responses": {
+          "200": {
+            "description": "Every client unpaired (possibly none)",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/UnpairAllResult"
+                }
+              }
+            }
+          },
+          "401": {
+            "description": "Missing or invalid bearer token",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/ApiError"
+                }
+              }
+            }
+          }
+        }
       }
     },
     "/api/v1/clients/{fingerprint}": {
@@ -1767,6 +1797,56 @@
             }
           }
         }
+      },
+      "delete": {
+        "tags": [
+          "native"
+        ],
+        "summary": "Unpair every native client",
+        "description": "The collection form of [`unpair_native_client`]: empties the punktfunk/1 trust store in ONE\npersisted write (not a loop of them — a failure partway would leave a half-emptied store), and\nends every live native session the removed clients own.\n\nIdempotent, hence a 200 rather than the single unpair's 204/404: an already-empty store\nsatisfies the request, and the count still tells the operator what it meant.",
+        "operationId": "unpairAllNativeClients",
+        "responses": {
+          "200": {
+            "description": "Every native client unpaired (possibly none)",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/UnpairAllResult"
+                }
+              }
+            }
+          },
+          "401": {
+            "description": "Missing or invalid bearer token",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/ApiError"
+                }
+              }
+            }
+          },
+          "500": {
+            "description": "Could not persist the trust store",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/ApiError"
+                }
+              }
+            }
+          },
+          "503": {
+            "description": "Native host not enabled",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/ApiError"
+                }
+              }
+            }
+          }
+        }
       }
     },
     "/api/v1/native/clients/{fingerprint}": {
@@ -7687,6 +7767,22 @@
           }
         }
       },
+      "UnpairAllResult": {
+        "type": "object",
+        "description": "What a bulk unpair removed. Shared by the two collection DELETEs (`/clients` and\n`/native/clients`) so the console sees one schema across both pairing planes.\n\nA count rather than 204: \"unpair everything\" is idempotent, so an empty store is a success, and\nthe operator still wants to be told whether that meant three devices or none.",
+        "required": [
+          "unpaired"
+        ],
+        "properties": {
+          "unpaired": {
+            "type": "integer",
+            "format": "int32",
+            "description": "Clients removed from the trust store — 0 when nothing was paired.",
+            "example": 3,
+            "minimum": 0
+          }
+        }
+      },
       "UpdateJobInfo": {
         "type": "object",
         "description": "A running apply job (or a spawned installer that hasn't resolved yet).",

docs/releases/v0.28.1.md

@@ -0,0 +1,64 @@
+Wire-compatible with 0.28.0 — everything you have already paired keeps working, and you can update one side at a time. Nothing here changes how a host and a client agree on what to send each other, so an old client on a new host, or the other way round, streams exactly as it does today.
+
+This is a fix release, and most of it is about things that were wrong in ways nothing announced. On Windows, your Steam library could stay completely empty after the last update, and a Punktfunk host sitting idle — nothing connected, nothing streaming — could wreck the frame rate of a game you were playing on that same machine. An Android TV box could be silent for a whole session; a Steam Deck's Punktfunk home would not open; games could not reach high dynamic range (HDR) at all on Linux machines running our own compositor, while the Steam interface in front of them glared; and an Apple TV was being pushed into HDR mode by streams that were not HDR at all, lifting blacks to grey.
+
+Several of these came from people who reported them carefully enough to be found. One of them, the crash that lost your game on reconnect, was tracked down, fixed and proven on his own hardware by **luxus** — that fix is in this release as he wrote it.
+
+## TL;DR
+
+- **On Windows, your Steam games went missing after updating to 0.28.0.** The Steam add-on could publish nothing, because Steam keeps its artwork in Program Files and the host was not allowed to read it. Fixed — and one unreadable cover no longer throws away the whole library with it.
+- **An idle Punktfunk host could ruin a game you were playing on that same machine**, down to 2–5 frames per second at worst, with nothing connected and no stream running. Two separate causes, both fixed, both reported from Helldivers 2.
+- **No sound at all on some Android TV boxes** — an NVIDIA Shield in particular — is fixed, and the app now recovers when your TV or receiver changes mode mid-stream instead of staying silent for the rest of the session.
+- **The Punktfunk home would not open on a Steam Deck after updating to 0.28.0.** That is fixed, along with the missing statistics overlay in streams that came from the same fault.
+- **Games can finally use high dynamic range on Linux hosts running Punktfunk's compositor.** They could not before, on essentially any machine, and nothing said so.
+- **HDR streams looked washed out while the Steam interface looked glaring** — one brightness mistake causing both, now corrected.
+- **On an Apple TV, ordinary streams were switching the television into HDR** and lifting blacks to grey — and those same streams were being drawn with no colour information at all.
+- **If your Apple device's statistics overlay ever showed impossibly good numbers, that is why** — three separate faults made those figures unreliable. Old measurements are worth re-taking.
+- **Streaming your desktop with the mouse pointer forwarded failed outright on Hyprland and Sway**, giving you a black picture. It affected every current install, not only old ones.
+
+## Before you update
+
+- **On Windows, two things in your Sound settings will look different, and both are deliberate.** "Speakers (Wireless Controller)" now shows as *disabled* whenever no controller is connected through Punktfunk — that is it parked out of the way of your local games, not a fault, and it comes back on its own. And Punktfunk no longer keeps your default microphone: it borrows it for the length of a stream and gives it back. If you actually want apps to record the client's microphone while nothing is streaming, select "Punktfunk Microphone" yourself — your choice will now be left alone.
+- **Only if you are coming from 0.27 or older:** read [the 0.28.0 notes](https://git.unom.io/unom/punktfunk/releases/tag/v0.28.0) first. That release has two things that need you to act — your game library now comes from add-ons you install per store (with none installed, your library is empty), and Moonlight-compatible connections became something you switch on. Neither applies if you are already on 0.28.0.
+
+## New
+
+- **Your saved hosts have a menu when you use a controller on Apple devices.** Press up on a host tile for Wake, Copy link, Edit, Forget pairing and Remove — the same menu the desktop and Android consoles already had, so all three work the same way. A renamed machine or a mistyped address used to stay wrong forever unless you switched to touch. Removing asks twice, deliberately, because a thumbstick from across the room deserves at least as much care as a dialog.
+- **The shortcut list is now a page you can open.** It used to appear as a banner over the stream for six seconds right after connecting — which is the one moment nobody is asking what the controls are. It lives in an About section you can visit whenever you want it.
+- **Unpair every device at once.** Clearing a host's paired devices meant deleting them one at a time, confirming each. There is now a single action for it on the Paired devices card, and it ends any live session belonging to a device it removes.
+
+## Improved
+
+- **High dynamic range brightness matches between host and client.** Anything that is not an HDR game — your desktop, the Steam overlay, an ordinary title — was being mapped nearly a stop brighter by the host than every Punktfunk client expects. That is what made the Steam interface look glaring and over-saturated while actual HDR game content looked flat and washed out on the same stream. Both come from the same mistake and both are fixed.
+- **Your host tells you when high dynamic range cannot work.** A session could start advertising HDR while having made it unreachable for every game inside it, with nothing anywhere explaining the washed-out result. It now says so.
+- **The on-screen statistics no longer double-count decoding.** On machines using the fastest decoding path, the stage breakdown listed a figure that was already included in another one, so the parts did not add up to the total and a reader who checked was right to be confused. It is now reported separately, labelled as the single sample it is.
+
+## Fixed
+
+- **On Windows, the Steam add-on synced nothing and your grid stayed empty.** Steam installs to Program Files and keeps its artwork there, and the host's list of places it is allowed to read art from covered the launchers that install per-user — but not Steam. Every cover the add-on offered was rejected, and because one bad cover failed the whole submission, that meant every Steam game rather than one thumbnail. Both halves are fixed: Steam's own install locations are now allowed (including on a second drive), and a cover that cannot be served is dropped so the rest of your library still arrives. This only affected Windows — every Steam layout on Linux was already covered — and it arrived with 0.28.0, when the built-in Steam scanner was replaced by the add-on.
+- **A Punktfunk host that was doing nothing at all could wreck a game running on the same Windows machine** — 2–5 frames per second at worst, with no client connected and no stream ever started. Two independent causes, both from the same set of reports: the host presents a controller speaker that looks exactly like a real DualSense's, and a game that finds it engages its DualSense audio path against a device nothing is feeding; and the host was claiming your default microphone permanently, so any game holding an open voice input stalled on a virtual mic that only runs during a stream. The controller speaker is now hidden except while a controller is actually attached, and your microphone is only borrowed for the length of a stream. Machines already stuck repair themselves on the next start.
+- **Streaming your desktop with the pointer forwarded gave a black picture on Hyprland and Sway.** Punktfunk asked the desktop's screen-sharing service for the pointer in a form neither compositor offers, and the request was refused before it ever reached them — so the whole capture failed rather than losing just the pointer. It now asks what is actually available and takes the best on offer. Measured against fully up-to-date Hyprland and portal versions: this was every current install, and updating them would not have helped. You will now see a single pointer drawn by the host instead of your client drawing its own.
+- **An Android TV box could have no audio for an entire session.** Reported on an NVIDIA Shield with a host and settings that played fine everywhere else, and video unaffected. The app asked Android for an audio device and then trusted the answer: a device that accepted the request but played nothing was never noticed, a device that refused to start disabled sound for the rest of the session, and — most common on a television — a device that went away during an HDMI mode change was never reopened. It now proves that sound is actually being taken before it accepts a device, and reopens automatically when your TV or receiver changes mode. TV boxes now use the ordinary shared audio path rather than the exclusive low-latency one, which was never buying them the latency it cost.
+- **The Punktfunk home would not open on a Steam Deck after updating to 0.28.0.** Both the Decky button and the library shortcut failed. The same fault silently removed the statistics and capture overlays inside streams on other machines. It came from a graphics library sizing itself to what the machine's graphics driver supported rather than to what Punktfunk had asked for, which only became a problem once drivers moved ahead of us.
+- **Games could not use high dynamic range on Linux hosts running Punktfunk's compositor** — on essentially every machine, not a rare configuration. Reaching HDR requires a small graphics component that has to match the compositor exactly, and we shipped the compositor without it, leaving the host guessing whether the one your distribution provided was compatible. Because we build our own compositor, that guess was almost always wrong in the direction of switching HDR off. We now ship the matching component ourselves, on every Linux packaging channel.
+- **Reconnecting after a disconnect could lose your game** on Linux hosts with an NVIDIA card. The host keeps your session alive when a client leaves so reconnecting resumes it, and the compositor could crash in exactly that window — so the session you came back to was a brand-new one with your game gone. Found, fixed and proven in the field by **luxus**, over an evening of Baldur's Gate 3 at 4K60 HDR that had produced four crashes before the fix and none after.
+- **A stream that was not HDR pushed an Apple TV into HDR mode anyway**, which switches the HDMI output to limited range — so on a television set for full range, black came out grey. The switch was triggered by your HDR *setting* being on rather than by the stream actually being HDR, and that setting is on by default.
+- **Ordinary streams on Apple devices were drawn with no colour information at all**, leaving them mildly over-saturated on a Mac or iPad with a wide-colour screen, and lifting blacks on an Apple TV. A stream that was not HDR from its very first frame skipped colour setup entirely.
+- **The statistics overlay on Apple devices reported numbers that could not be true** — a network figure lower than the host's own encoding time, and historically readings of zero. Three faults: the clock difference with the host was measured once at connect and never updated (it drifts, and on a virtual-machine host it jumps), impossible samples were being discarded silently rather than invalidating the reading, and several unavailable values printed as "NaN". The overlay now warns you when a reading is suspect instead of showing a plausible wrong number.
+- **AV1 streams fell back to slower decoding** on hardware that decodes them perfectly well. Some encoders mark a stream as "not restricted to any quality level", and that marker was being read as a level so high that no device could claim to support it.
+- **On Apple TV, console text could be white on a pale background**, making screens unreadable with the light appearance.
+- **Punktfunk add-ons could not be installed on NixOS**, where the component that manages them was reported missing on machines where it was installed, enabled and running.
+- **On NixOS the host could crash-loop forever, unable to claim its own ports.** A second copy was being started under the root account — which springs into life the moment anyone signs in as root — and it won the race for the ports the real one needed. The log blamed some other program, because a second copy of itself is the last thing anyone looks for. The service is now scoped to the accounts you list.
+- **Two host warnings blamed the wrong thing.** One announced a "metronomic" disturbance from your display hardware when the regular timing was in fact a client's own recovery interval; the other reported catastrophic audio loss between sessions, when what it had counted was silence during the seconds no one was connected. Neither ever indicated a real fault.
+
+## Thanks
+
+**luxus** found the crash that lost your game on reconnect, wrote the fix, and proved it on his own machine — an evening of Baldur's Gate 3 at 4K60 HDR that had produced four crashes before it and none after. It ships here as he wrote it.
+
+Most of the rest of this release exists because people took the trouble to report a fault precisely: the silent Android TV box, the empty Steam library, the game stuttering next to an idle host, the washed-out HDR, the black picture on Hyprland. Thank you — that detail is what makes a fault findable.
+
+## For developers
+
+Protocol, ABI, driver and embedder detail — including the version table and the (empty) breaking-changes list — is in [CHANGELOG.md](https://git.unom.io/unom/punktfunk/src/tag/v0.28.1/CHANGELOG.md).
+
+Nothing breaks: the wire protocol, the C ABI, the virtual-display driver protocol and the plugin contract are all unchanged from v0.28.0. Two things are worth reading if they apply to you: every Linux packaging channel now ships a second gamescope artifact and a package without it fails to build rather than degrading quietly, and Android's `nativeStartAudio` takes one more argument.

docs/releases/whatsnew/v0.28.1.txt

@@ -0,0 +1,3 @@
+• Fixes having no sound at all on some Android TV boxes, the NVIDIA Shield among them. The app now checks that your TV or receiver is really taking the audio, instead of trusting that it will.
+• Sound returns on its own when your TV or receiver changes mode during a stream. Before, it could stay silent for the rest of the session.
+• A stream that loses audio now says so, rather than looking exactly like an app with nothing to play.

packaging/nix/README.md

@@ -64,7 +64,7 @@ Add the flake and enable the host and/or client:
         ({ ... }: {
           services.punktfunk.host = {
             enable = true;
-            users = [ "alice" ];        # → added to the `input` group for virtual gamepads
+            users = [ "alice" ];        # → `input` group for gamepads, AND scopes the units to alice
             openFirewall = true;        # native + GameStream ports
             desktopSession = true;      # a machine you log into — restart the host with the desktop
             settings = {
@@ -236,6 +236,14 @@ services.punktfunk.host = {
 users.users.streamer.linger = true;
 ```
 
+**Set `users` whenever `autoStart` is on.** `systemd.user.*` installs into *every* user's systemd
+manager — root's included, and root gets one the moment anybody logs in as root. Without `users` to
+scope them, `autoStart` therefore starts a *second* host in root's manager, which wins the race for
+the fixed ports and leaves the real one restarting forever on `bind RTSP 48010: Address already in
+use` (every other listener having bound fine, so it reads like a clash with an unrelated program).
+The module renders `ConditionUser=` from this list to prevent that; with the list empty it falls
+back to refusing system users, which keeps root out but cannot tell two logins apart.
+
 Leave `desktopSession` off here — an appliance starts its own compositor and may never reach
 `graphical-session.target`, which would leave the host permanently stopped. `gamescopeHdr` (on by
 default) already puts the patched `punktfunk-gamescope` on the service PATH, so the gamescope

packaging/nix/module-check.nix

@@ -143,6 +143,39 @@ let
       ok = failedAssertions clientOnly == [ ];
     }
 
+    # --- user scoping: the second-copy-steals-the-ports trap -----------------------------------
+    # `systemd.user.*` installs into EVERY user's manager, root's included (user@0.service exists
+    # as soon as anyone logs in as root), and `autoStart` puts these in default.target. Root's host
+    # then wins the fixed ports and the desktop user's restarts forever on
+    # `bind RTSP 48010: Address already in use` — every other listener in its log having bound
+    # fine, so it reads like an unrelated program. MEASURED on a real box before this was fixed.
+    {
+      # `|` = TRIGGERING condition, which systemd ORs. Plain repeated ConditionUser= lines are
+      # ANDed and would match nobody — the whole reason the prefix is there.
+      name = "host.users scopes every user unit to those users, OR-ed";
+      ok =
+        let
+          scoped = name: has desktop name "ConditionUser=|alice";
+        in
+        scoped "punktfunk-host" && scoped "punktfunk-web" && scoped "punktfunk-scripting";
+    }
+    {
+      # web-init already carried a ConditionPathExists. That one is NON-triggering, so systemd
+      # requires it AND at least one triggering user condition — adding ours must not drop it.
+      name = "web-init keeps its path condition alongside the user scope";
+      ok =
+        has desktop "punktfunk-web-init" "ConditionUser=|alice"
+        && has desktop "punktfunk-web-init" "ConditionPathExists=!%h/.config/punktfunk/web-password";
+    }
+    {
+      # With no host.users to name, still keep SYSTEM users (root) out, while leaving the module
+      # header's manual `systemctl --user enable --now punktfunk-host` working for a normal login.
+      name = "with no host.users, the units still refuse system users (root)";
+      ok =
+        has appliance "punktfunk-host" "ConditionUser=!@system"
+        && !(has appliance "punktfunk-host" "ConditionUser=|");
+    }
+
     # --- the KWin identification trap (packaging/arch/punktfunk-host.install) -------------------
     # The host MUST exec the plain store path. A capability wrapper here would put CAP_SYS_NICE in
     # the process's permitted set, and the kernel then refuses KWin the /proc/<pid>/exe readlink it

packaging/nix/nixos-module.nix

@@ -55,6 +55,27 @@ let
 
   hostSettingsFile = pkgs.writeText "punktfunk-host.env" (renderEnv cfg.host.settings);
 
+  # WHICH users' `systemd --user` instances may run these units — and why they need saying at all.
+  #
+  # `systemd.user.*` installs into EVERY user's manager; there is no per-user form of it in NixOS.
+  # Combined with `autoStart` putting the units in `default.target`, that includes **root**, whose
+  # `user@0.service` springs into existence the moment anybody so much as SSHes in as root. Root's
+  # copy of the host then wins the race for the fixed ports and the desktop user's copy fails
+  # forever on `bind RTSP 48010: Address already in use` — with every other listener in its log
+  # having bound fine, so it reads like a clash with some unrelated program rather than a second
+  # copy of itself. MEASURED 2026-08-14 on a fresh NixOS 26.05 box.
+  #
+  # `host.users` is already documented as "the host runs as these users' systemd --user service",
+  # so it is the right scope. When it is empty we cannot name the intended user, so fall back to
+  # excluding system users — which is precisely what keeps root out — and leave the module header's
+  # manual `systemctl --user enable --now punktfunk-host` route working for any normal login.
+  #
+  # ⚠ The `|` prefix is load-bearing: it makes each entry a TRIGGERING condition, and systemd ORs
+  # those. Plain repeated `ConditionUser=` lines are ANDed, so a two-user list would match NOBODY.
+  # Non-triggering conditions on the same unit (punktfunk-web-init's ConditionPathExists) still
+  # have to hold, which is the behaviour we want.
+  userScope = if cfg.host.users == [ ] then [ "!@system" ] else map (u: "|${u}") cfg.host.users;
+
   # Native punktfunk/1 ports (control plane + discovery + mgmt API). The media data plane is an
   # ephemeral per-session UDP port the host hole-punches, so nothing fixed to open (see
   # packaging/linux/punktfunk.ufw).
@@ -106,6 +127,10 @@ in
           Start the host automatically in every user's graphical session (adds it to the user
           `default.target`). For a login-less appliance, also enable lingering for the host user
           (`users.users.<name>.linger = true`) so the user service comes up at boot.
+
+          "Every user" is bounded by `host.users` via `ConditionUser=` — without that bound this
+          option also starts a host in ROOT's user manager the moment anybody logs in as root, and
+          that copy takes the ports from the real one. Set `host.users` on a multi-user box.
         '';
       };
 
@@ -147,6 +172,15 @@ in
           usbip/vhci nodes the virtual Steam Deck pad attaches through. The second is separate on
           purpose — it can emulate arbitrary USB hardware, so only list users you would trust with
           that. The host runs as these users' `systemd --user` service.
+
+          This list ALSO scopes the units themselves: they carry a `ConditionUser=` for these
+          users, so no other user's `systemd --user` instance can start them. That matters because
+          `systemd.user.*` installs into every user's manager — including root's, which exists as
+          soon as anyone logs in as root — and a second host silently wins the race for the fixed
+          ports, leaving the real one restarting forever on "Address already in use".
+
+          Left empty, the units are merely refused to SYSTEM users (`ConditionUser=!@system`), so
+          any normal login can still run the host by hand and root still cannot.
         '';
       };
 
@@ -466,6 +500,9 @@ in
       systemd.user.services.punktfunk-host = {
         description = "punktfunk GameStream + punktfunk/1 streaming host";
         documentation = [ "https://git.unom.io/unom/punktfunk" ];
+        # Keep root (and every other system user) from starting a second host that steals the
+        # fixed ports from the desktop user's — see `userScope`.
+        unitConfig.ConditionUser = userScope;
         # Soft ordering: the host listens immediately and only touches the compositor per session.
         after = [ "pipewire.service" ] ++ optional cfg.host.desktopSession "graphical-session.target";
         wants = [ "pipewire.service" ];
@@ -573,7 +610,12 @@ in
       systemd.user.services.punktfunk-web-init = {
         description = "punktfunk web console first-run setup (login password)";
         documentation = [ "https://git.unom.io/unom/punktfunk" ];
-        unitConfig.ConditionPathExists = "!%h/.config/punktfunk/web-password";
+        # ⚠ ConditionUser here is TRIGGERING (`|`) and ConditionPathExists is not, so systemd
+        # requires the path condition AND at least one user condition — which is the intent.
+        unitConfig = {
+          ConditionPathExists = "!%h/.config/punktfunk/web-password";
+          ConditionUser = userScope;
+        };
         path = [ pkgs.coreutils ];
         serviceConfig = {
           Type = "oneshot";
@@ -589,6 +631,8 @@ in
       systemd.user.services.punktfunk-web = {
         description = "punktfunk management web console";
         documentation = [ "https://git.unom.io/unom/punktfunk" ];
+        # Same scoping as the host: root's instance would take 47992 from the real one.
+        unitConfig.ConditionUser = userScope;
         after = [
           "punktfunk-web-init.service"
           "punktfunk-host.service"
@@ -640,6 +684,8 @@ in
       systemd.user.services.punktfunk-scripting = {
         description = "punktfunk plugin/script runner";
         documentation = [ "https://git.unom.io/unom/punktfunk" ];
+        # Same scoping as the host: a root-side runner would talk to the wrong session's mgmt API.
+        unitConfig.ConditionUser = userScope;
         # Plugins talk to the host's loopback mgmt API; order after it (soft — the runner backs off
         # and retries per unit, so this is ordering only, not a hard requirement).
         after = [ "punktfunk-host.service" ];